UC-NRLF 


2ME    Mflfl 


UNIVERSITY  OF  CALIFORNIA. 


r  ilKT  OR 


Receive  J 
Accession 


Clots  No. 


A    GUIDE 


TO 


ELEMENTARY  CHEMISTRY 


FOR     BEGINNERS 


BY 

LE    ROY    C.   COOLEY,   PH.D., 

PROFESSOR    OF    PHYSICS    AND     CHEMISTRY    IN    VASSAR    COLLEGE 


$3 

pmntaiTT 


NEW  YORK    .:•    CINCINNATI     •:•    CHICAGO 

AMERICAN    BOOK    COMPANY 


0 


0 


COPYRIGHT,  1886, 
BY   IV1SON.    BLAKEMAN,   TAYLOR,   &  TO. 

M.    i 


UNIVERSITY 


PREFACE. 


IN  an  Elementary  Chemistry,  written  in  1872,  it  was  my 
purpose  to  give  a  short  course,  for  beginners,  in  which  the 
experimental  evidence,  on  which  the  most  fundamental  parts 
of  the  science  rested,  should  take  the  place  of  minute  details 
and  advanced  theoretical  discussions,  hoping  in  this  way  to 
encourage  the  study  of  chemistry  by  experiment  instead  of  by 
books  alone,  as  was  so  much  the  custom  at  that  day.  A  Student's 
Guide,  printed  for  the  use  of  my  classes  in  1878,  contained  a 
course  introductory  to  qualitative  analysis,  giving  the  student 
nothing  but  an  outline  of  experiments.  He  was  expected 
to  make  the  experiments,  to  observe  and  describe  his  own- 
results,  and  from  these  to  construct  for  himself  a  plan  for  the 
detection  of  the  metals.  I  now  combine  the  leading  ideas  of 
those  two  books,  and  offer  to  my  fellow-teachers  a  new  volume, 
in  which  they  are  more  fully  developed  in  ways  suggested  by 
the  unbroken  experience  of  the  intervening  years. 

Chemistry  as  a  branch  of  study  in  the  schools  has  two  great 
merits  happily  combined.  One  is  to  be  found  in  the  kind  of 
knowledge  it  offers,  and  the  other  in  the  peculiar  mental 
training  it  affords.  Of  these  the  latter  is  certainly  not  the 
least  important,  because  a  person  is  well  educated,  not  so 
much  in  proportion  to  what  he  knows,  as  in  proportion  to 
what  he  can  do  with  his  knowledge.  Hence  a  chief  purpose 

iii 


IV  PREFACE. 

of  the  study  of  elementary  chemistry  in  schools  is  to  educate 
the  mind  by  giving  it  the  right  kind  of  exercise  in  the  use  of 
its  powers. 

I  have  therefore  tried  to  make  a  judicious  selection  of  the 
most  fundamental  facts  and  principles  of  chemistry,  and  to 
present  these  in  such  a  way  that  the  student  must  constantly 
use  his  senses  to  discover  facts,  his  reason  in  drawing  correct 
inferences  from  the  data  he  collects,  and  good  English  in  ex- 
pressing accurately  what  lie  sees  and  thinks. 

I  know  of  but  one  way  to  teach  a  student  how  to  acquire 
a  real  knowledge  of  nature,  and  that  is,  to  fix  his  mind  habit- 
ually on  things  and  events  brought  under  his  own  eye,  and 
direct  him  to  the  discovery  of  facts  and  principles  for  himself. 
The  use  of  apparatus  is,  of  course,  indispensable  if  the 
student  is  thus  to  study  phenomena  instead  of  descriptions 
of  phenomena,  and  the  use  of  apparatus,  by  himself,  is  with- 
out doubt  the  method  which  is  most  certain  to  stimulate  his 
mind  to  the  greatest  activity.  Laboratory  study  for  students 
in  high  schools  is  rapidly  growing  in  favor,  but  unfortunately, 
in  many  schools  where  chemistry  is  taught,  the  difficulties  in 
the  way  of  this  method  are  still  thought  to  be  real.  Even  in 
these,  chemistry  to  be  truly  useful  should  be  presented  as  a 
study  of  phenomena,  by  experiments,  instead  of  what  some- 
body has  said  about  phenomena  in  books. 

I  have  therefore  tried  to  construct  a  course  of  experiments 
suited  to  the  use  of  the  beginner,  at  his  laboratory  desk,  and 
to  the  use  of  the  teacher  for  his  class  of  beginners,  where 
facilities  for  students  to  work  for  themselves  seem  to  be  out 
of  reach. 

The  study  of  any  subject  by  experiment  combines  two  kinds 
of  exercise;  mechanical  and  mental  operations  go  hand  in 
hand.  On  this  account  experimental  investigation  is  a  com- 


PREFACE.  V 

plex  and  difficult  work.  All  that  can  be  done  to  make  it  less 
so  for  beginners  is  to  make  one  or  the  other,  the  mechanical 
or  the  mental  processes,  predominate  in  our  elementary  course 
of  instruction.  Then  which  shall  it  be?  The  mechanical  of 
course  stands  first,  in  one  sense,  for  there  will  be  no  phenomena 
to  study  until  apparatus  is  selected  and  arranged  to  exhibit 
them.  But,  on  the  other  hand,  a  wise  selection  of  apparatus 
and  conditions  cannot  be  made  by  one  who  has  not  already 
acquired  some  skill  in  tracing  the  relations  of  cause  and  effect, 
and  some  experience  in  the  application  of  experimental 
methods.  I  think  we  should  first  cultivate  the  power  to 
observe  exhaustively  and  to  detect  relations,  —  that  we  should 
make  the  mental  more  prominent  than  the  mechanical  in  the 
elementary  study  of  chemistry.  Accordingly : 

In  this  course  of  experiments  the  mechanical  operations 
are  described  in  quite  minute  details.  Exactly  what  is  to  be 
done  is  told,  but  what  is  to  happen,  and  the  meaning  of  it,  is 
for  a  time  withheld.  Exceptions  to  this  plan  will  be  found 
in  the  description  of  processes  which  are  simply  means  to 
secure  conditions,  and  in  the  statement  of  facts  which  may  be 
needed  for  immediate  use.  But  in  general  the  phenomena 
which  hold  the  chemistry  of  substances  or  processes  are  left 
for  the  student  to  discover.  See,  for  example,  page  35,  or 
pages  85,  86. 

I  know  that  much  stress  is,  by  many,  laid  upon  the  industrial 
value  of  an  instrument-making  course  in  chemistry.  But  it 
seems  to  me  that  the  study  of  chemistry  is  not  primarily  to 
teach  mechanics,  and  that  the  use  of  tools  and  the  possession 
of  mechanical  ingenuity  can  be  better  acquired  in  the  indus- 
trial school  or  workshop,  where  these  are  the  specific  aims, 
than  in  the  laboratory  of  the  high  school  or  academy,  where 
the  acquisition  of  knowledge  for  the  sake  of  mental  training  is 


VI  PREFA  CE. 

the  chief  purpose.  Home-made  apparatus  is  not  to  he  de- 
spised, but  to  he  greatly  respected,  where  nothing  hetter  can  be 
had,  for  much  can  be  done  with  the  most  common  utensils, 
such  as  bottles,  fruit-jars,  tea-saucers,  and  oyster-cans.  But 
certainly  beginners  can  do  hetter  work  with  good  facilities  than 
with  poor  ones.  And  while  there  is  so  much  in  the  market 
which  is  at  once  scientific  and  inexpensive,  the  student  should 
be  taught  to  reach  more  accurate  results  than  are  otherwise 
possible  by  the  use  of  it.  Productive  ingenuity  and  skill 
must  be  founded  on  exact  knowledge  and  clear  thinking;  they 
cannot  precede  these.  Therefore  : 

The  apparatus  called  for  in  this  course  has  been  selected 
from  that  which  is  made  for,  and  approved  by,  chemists.  The 
pieces  are  neat,  simple,  easily  put  together,  always  in  market, 
and  as  cheap  as  possible  for  good  scientific  work.  (See  Appen- 
dix, Fig.  69.) 

A  brief  summary  of  the  most  important  facts  and  principles 
follows  the  experimental  work,  by  which  the  student  can  check 
and  correct  his  results.  In  this  summary  will  be  found  the 
information  which  should  be  acquired  by  beginners  in  chem- 
istry. I  have  tried  to  include  in  it  only  such  things  as  will  be 
of  most  value  to  the  many  who  will  finish  the  study  of  chem- 
istry in  the  high  school,  and  to  the  few  also  who  are  there  to 
lay  a  foundation  for  college  work.  "Not  how  much  wre  know 
is  the  best  question,  but  how  we  have  got  what  we  know,  and 
what  we  can  do  with  it,  and,  above  all,  what  it  has  made  of 
us."  —  J.  P.  LESLIE. 

It  is  not  well  to  undertake  too  much.  It  is  not  best  to  have 
the  student's  text-book  burdened  with  matter  which  he  is  not 
expected  to  master.  There  is  more  education  to  be  gained  by 
extending  the  search  for  facts  into  other  volumes  than  by 
skipping  parts  of  the  book  in  .use.  I  have  not  given  a  long1 


*.  vn 

list  of  experiments,  but  have  tried  to  make  a  judicious  selection, 
believing  that  a  few  typical  ones  well  made  and  thoroughly 
studied,  are  far  more  useful  than  a  larger  number  would  be 
if  studied  in  haste.  What  I  mean  by  the  thorough  study  of  a 
few  experiments  in  the  treatment  of  a  subject  may  be  seen  by 
referring  to  " Substitution,"  pp.  19-21:  "Decomposition  of  nitric 
acid,"  pp.  92-95;  or  "Chlorides,"  pp.  141-145. 

Additional  work  is  better  when  provided  by  teachers  for  such 
pupils  or  classes  as  have  time  or  talent  to  undertake  it.  I 
would  make  such  work  partake  of  the  nature  of  research  as 
much  as  possible.  A  student  may  be  given  some  question  to 
be  answered  by  his  own  experiments,  or  two  substances  whose 
mutual  reactions  and  results  he  is  directed  to  investigate,  or 
a  single  body  whose  properties  he  is  asked  to  study  and  report. 
Some  work  of  this  kind  I  have  given  under  the  head  of  "  Ex- 
ercises." (See,  for  examples,  pp.  39,  82, 100.) 

Next  in  value  to  research  in  the  laboratory  stands  research 
in  the  library.  By  all  means  teach  the  student  how  to  make 
the  results  of  his  study,  with  apparatus  and  the  text-book,  the 
nucleus  around  which  to  group  other  facts,  a  center  from 
which  to  extend  his  knowledge.  From  the  following  works 
the  teacher  can  select  abundant  materials  for  this  exercise,  in 
kind  and  quantity  suited  to  the  varying  wants  of  different 
individuals  or  of  successive  classes.  Buckley's  "  Short  History 
of  Natural  Science."  Wurtz'  "History  of  Chemical  Theory." 
Wurtz'  "Atomic  Theory."  Cooley's  "New  Text-Book  of 
Chemistry."  Cooke's  "New  Chemistry."  Remsen's  "Or- 
ganic Chemistry."  Remsen's  "  Theoretical  Chemistry."  Ros- 
coe  and  Schorlemmer's  "  Treatise  on  Chemistry."  Fresenius' 
"Qualitative  Analysis."  Douglas  and  Prescott's  "Qualitative 
Analysis." 


viii  PREFACE. 

1  have  in  all  cases  rejected  dangerous  experiments,  but  I 
have  in  many  cases  devised  simple,  safe,  and  efficient  ways  to 
study  explosive  and  noxious  substances.  See,  for  examples, 
Hydrogen,  pp.  29,  30,  and  Chlorine,  pp.  138,  139. 

The  wood-cuts  which  represent  the  experiments  are,  with 
a  single  exception,  Fig.  23,  made  from  the  photographs  or 
drawings  of  the  apparatus  in  actual  use.  For  the  selected  cuts, 
which  illustrate  the  descriptions  of  historical  or  industrial 
work,  I  am  unable  to  give  the  credit  which  is  due  to  their 

unknown  authors. 

L.  C.  C. 
POCOHKEEPSIE,  June,  1886. 


TJHI7BRSIT7 


CONTENTS. 


OBSERVATION    AND    EXPERIMENT. 

PAGE 

Chemistry :   Observation ;  experiment ;  way  to  study  .    .      9 

CHEMICAL,    CHANGES. 

Decomposition ;  combination  ;  substitution ;  double  decom- 
position ;  heat  and  chemical  action ;  electricity  and 
chemical  action;  light  and  chemical  action  ....  13 

Hydrogen:  Preparation  of;  properties  of;  cause  of  the 
explosion  of;  water  a  product  of  its  combustion;  heat  a 
product  of  its  combustion 28 

Oxygen:   Preparation  of;  properties  of;  chemical  actions 
of;  occurrence  of;  allotropism  of;  ozone 33 

Exercises  :  Experimental  study  of  chemical  changes  .    .    39 

CHEMISTRY    OF    COMBUSTION. 

Burning  of  a  candle  ;  burning  of  other  substances ;  material 
products;  heat  also  a  product;  light  also  a  product; 
structure  of  flame ;  queries 41 

CHEMISTRY    OF    WATER. 

Analysis  and  synthesis;  analysis  of  water;  composition  of 
water  by  weight;  percentage  composition;  composition 
by  volume;  constant  composition  of  water;  constant 
composition  of  other  compounds ;  the  LAW  of  constant 
composition ;  water  in  nature  ;  solvent  power  of  water ; 
drinking  waters ;  mineral  waters ;  effect  of  cold  on 
water 50 

Exercises  :   Experimental  investigations 63 

ix 


X  CONTENTS. 

CHEMISTRY    OF    THE    ATMOSPHERE. 

PAGE 

Lavoisier's  experiment;  oxygen  removed  from  air  by  sul- 
phur and  by  phosphorus 65 

Nitrogen:    Preparation  of;  properties  of;  AIR:  analysis 
of;  composition  of;  a  mixture ;  diffusion  of  gases  ...    66 

Respiration:  Of  animals;  produces  changes  in  air; 
ventilation ;  of  plants 77 

Exercises  :  Investigations  —  the  action  of  sulphuric  on 
oxalic  acid  and  the  action  of  phosphorus  on  air .  .  .  82 

COMPOUNDS  OF  NITROGEN,  HYDROGEN,  AND  OXYGEN. 

Office  of  nitrogen  in  the  air ;  character  of  the  compounds 
of  nitrogen 84 

Ammonia:  Production  of  ammonia;  the  nascent  state; 
ammonia  in  gas-works ;  preparation  of  ammonia;  prop- 
erties of  ammonia;  its  action  on  the  acids;  composition 
by  volume 84 

Nitric  Acid:  Occurrence  of,  in  nature;  made  from 
sodium  nitrate;  properties  of;  decomposition  of;  the 
nitrates 90 

Nitrogen  Oxides :  Study  of  the  decomposition  of  nitric 
acid  by  copper ;  proof  that  air  takes  part  in  the  action ; 
the  several  products;  nitrous  oxide;  five  nitrogen 
oxides;  the  LAW  of  multiple  proportions;  combining 
weights .  .  92 

Exercises :  Investigation  of  tests 98 

THE    COMPOSITION    OF    PLANTS. 
Decomposition  of  wood  by  heat ;  constituents  of  plants  .    .  101 

Carbon :  Source  of  carbon  in  plants ;  charcoal-making ; 
lamp-black;  action  of  charcoal  on  gases;  action  of 
charcoal  on  colors  ;  action  of  charcoal  on  oxides ;  the 
diamond ;  graphite ;  allotropism  of  carbon 103 


CONTENTS.  XI 

PAGE 

Carbon  dioxide:  Preparation  of;  properties  of;  carbon 
monoxide ;  compounds  of  carbon  and  hydrogen ; 
methane 112 

ELEMENTS,    MOLECULES,    AND    ATOMS. 

The  number  of  the  ELEMENTS;  table  of  names,  symbols, 
and  atomic  weights ;  three  forms  of  matter ;  facts,  laws, 
and  theories,  to  be  carefully  distinguished.  MOLE- 
CULES; some  facts  about  the  expansion  of  gases;  the 
theory;  chemical  changes  are  changes  in  molecules; 
ATOMS;  "multiple  proportions"  explained;  atomic 
theory ;  symbols ;  formulas ;  atomic  weights ;  molecular 
weights;  reactions 117 

ACIDS,    BASES,    AND    SALTS. 

Acids;  salts;  hydroxides;  reaction  of  acids  and  bases; 
neutral  compounds 129 

Chemical  names :  Of  acids ;  of  salts ;  of  bases  ....  135 

CHLORINE  AND  THE  CHLORIDES. 
Discovery  of  chlorine;  preparation  and  properties  of 
chlorine ;  bleaching ;  the  CHLORIDES  ;  chlorides  by 
chlorine  water ;  chlorides  by  hydrochloric  acid;  chlorides 
by  aqua  regia ;  two  chlorides  of  one  metal ;  HYDROGEN 
CHLORIDE  :  Preparation  of;  composition  of;  comparison 
of  volume;  composition  of  compounds;  the  "two-vol- 
ume "  law  deduced ;  test  for  chlorine  and  the  chlorides  .  138 

The  Chlorine  Group:  Bromine;  iodine;  fluorine; 
their  hydrogen  compounds ;  relation  of  atomic  weights 
to  properties 147 

Exercises :  Study  of  tests 151 

SULPHUR  AND  ITS  COMPOUNDS. 

Native  sulphur  and  sulphides;  preparation  of  sulphur; 
properties  of  sulphur;  artificial  sulphides;  HYDROGEN 
SULPHIDE  :  preparation  and  properties  of;  use  of  .  .  .154 


xii  CONTENTS. 

PAGE 

The  Sulphur  Group:  Selenium;  tellurium;  hydrogen 
compounds;  general  behavior;  relation  of  atomic 
weights  to  properties 161 

Sulphurous  Oxide  and  Acid :  Preparation  of  sulphur- 
ous oxide;  properties  of  sulphurous  oxide;  sulphurous 
acid;  bleaching 163 

Sulphuric  Acid  and  the  Sulphates:  Properties  of 
the  acid ;  uses  of  the  acid ;  test  for  the  acid ;  manufac- 
ture of  the  acid ;  the  SULPHATES  :  sulphates  by  action 
of  the  acid  on  metals ;  by  action  of  the  acid  on  bases ; 
two  sulphates  of  the  same  metal ;  other  sulphur  acids  .  166 

Exercises:   Investigation  of  tests     .    .    *    » 173 

PHOSPHORUS,    AND    THE    NITROGEN    GROUP. 

Discovery  of  phosphorus;  properties;  red  phosphorus; 
matches ;  phosphorus  oxides  and  acids ;  the  phosphates ; 
manufacture  of  phosphorus 175 

Arsenic:  Arsenous  oxide;  arsenic  oxide;  arsenic  and 
hydrogen;  Marsh's  test 178 

The  Nitrogen  Group :  Members ;  their  hydrogen  com- 
pounds ;  relation  of  atomic  weights  to  properties  .  .  182 

SILICON,    AND    THE    CARBON    GROUP. 

Silicon :  Its  oxide  ;  the  CARBON  GROUP  :  members ;  their 
hydrogen  compounds;  their  oxygen  compounds;  the 
silicates 183 

Boron :  The  element ;  borax ;  boric  acid ;  no  hydrogen 
compound 185 

VALENCE. 

A  difference  in  atoms;  valence  defined;  substitution 
governed  by  valence;  the  valence  of  boron;  valence 
useful  in  study  of  reactions;  valence  of  an  element 
changes .  »  .  188 


CONTENTS.  xiii 

THE    METALS. 

PAGE 

What  is  a  metal?  number  and  abundance  of  the  metals; 
occurrence  in  nature 192 

THE    POTASSIUM    GROUP. 

Potassium:  Description  of;  chemical  action  on  water; 
occurrence  in  nature;  potassium  carbonate;  potassium 
hydroxide;  experiments  in  the  preparation  of  some 
other  salts ;  flame  test 195 

Sodium:  Description  of;  occurrence  in  nature;  sodium 
carbonate;  sodium  hydroxide;  flame  test;  study  of 
reaction  of  sodium  compounds 199 

Ammonium:  Facts  about  ammonia;  comparison  of 
formulas;  the  hypothetical  metal;  its  salts;  the  sul- 
phides ;  study  of  reactions  of  ammonium  compounds  .  201 

The  Potassium  Group :  Names  of  members ;  compari- 
son of  properties 204 

THE    CALCIUM    GROUP. 

Calcium:  The  metal;  its  occurrence  in  nature;  effect  of 
heat  011  the  carbonate;  effect  of  acids  on  the  carbonate; 
effect  of  water  on  the  carbonate ;  the  sulphate ;  to  pre- 
pare the  insoluble  compounds;  to  prepare  the  soluble 
compounds 206 

The  Calcium  Group:  Names  of  the  members;  com- 
parison of  atomic  weights  and  properties ;  study  of 
characteristic  reactions;  flame  colors 210 

METALS    OF    THE    ZINC    GROUP. 

Magnesium:  The  metal;  its  compounds ;  study  of  reac- 
tions of  magnesium  compounds 212 

Zinc:  The  metal;  manufacture  of;  uses  of;  compounds 
of;  preparation  of  insoluble  compounds,  and  study  of 
characteristic  reactions ;  the  zinc  group 212 


XIV  CONTENTS. 

THE    IRON    GROUP. 

PAGE 

Manganese:  The  metal;  its  oxides;  the  potassium  man- 
ganate  and  permanganate;  study  of  reactions  with 
manganese  salts;  COBALT;  NICKEL 217 

Iron:  Occurrence  of  iron  ;  its  ores;  roasting  and  reducing 
the  ores ;  cast-iron ;  the  three  forms  of  iron ;  manufac- 
ture of  wrought-iron;  manufacture  of  steel,  Bessemer 
process;  cementation;  compounds  of  iron ;  two  classes; 
the  two  chlorides;  distinctive  reactions  for  the  two 
classes ;  general  reactions  of  iron  salts 220 

Chromium:  The  metal ;  its  ore ;  the  potassium  chromate ; 
the  dichromate ;  reactions  of  chromium  salts  ....  229 

The  Iron  Group :  comparison  of  properties 231 

ALUMINUM. 

The  metal;  alum;  aluminum  oxide;  study  of  reactions 
of  aluminum  salts 233 

THE    ANTIMONY    GROUP. 

Antimony:  The  metal;  alloys  of;  BISMUTH;  the  anti- 
mony group ;  the  reactions  of  arsenic,  antimony,  and 
bismuth  compared 235 

TIN    AND    LEAD. 

Tin:  Occurrence  in  nature;  extraction  from  the  ore; 
properties  of  the  metal ;  compounds  of  tin ;  distinctive 
reaction  for  oiis  and  ic  compounds ;  general  reactions  of 
the  salts  of  tin 239 

Lead:  Occurrence  in  nature;  extraction  from  the  ore; 
two  methods ;  lead  oxides ;  lead  carbonate ;  reactions  of 
the  salts  of  lead 242 

THE    COPPER    GROUP. 

Copper:  Occurrence  in  nature;  extraction  from  its  ores; 
properties  of  the  metal ;  copper  compounds ;  the  sul- 
phate ;  study  of  reactions  of  the  salts  of  copper  .  .  .  247 


CONTENTS.  XV 

PAGE 

Mercury:  Occurrence  in  nature;  extraction  from  its  ore; 
properties  of  the  metal;  compounds  of  mercury;  the 
two  chlorides;  mercurous  compounds;  mercuric  com- 
pounds ;  study  of  reactions 251 

Silver:  Occurrence  in  nature;  extraction  from  its  sul- 
phide ;  extraction  from  galena ;  properties  of  the  metal  ; 
compounds  of  silver ;  reactions  of  the  salts  of  silver  .  .  254 

GOLD    AND    PLATINUM. 

Gold:   Occurrence  in  nature;    obtained  by  "washing"; 

obtained  by  "  amalgamation  " ;  properties  of  gold     .    .  259 
Platinum:     Occurrence    in    nature;    properties    of    the 

metal;  the  platinum  group 260 

CLASSIFICATION. 

Classes:  How  they  are  made;  the  classes  of  the  non- 
metals  founded  on  valence;  metals  not  always  classed 
in  this  way ;  more  than  one  way  to  group  the  metals ; 
four  principal  ways  to  classify  the  metals 262 

The  Natural  System:  Classification  by  atomic  weights; 
Newland's  discovery;  Mendelejeft's  extension;  the  spiral 
of  elements ;  the  vacant  places 264 

The  Analytical  System :  Classification  founded  on  solu- 
bilities; analytical  table  drawn  from  the  preceding  ex- 
periments in  this  course ;  how  to  find  out  what  metal  a 
compound  contains ;  making  notes  ;  to  identify  the  acid 
part;  to  name  the  salt;  hint  for  further  work;  form 
of  notes .  .  .  .  268 


ELEMENTARY    CHEMISTRY 


OBSERVATION    AND    EXPERIMENT. 

IN  the  study  of  Chemistry  we  are  to  learn  some  things 
about  the  different  kinds  of  matter.  There  are  two  ways 
in  which  these  things  have  been  found  out,  and  in  these 
same  ways  we  can  most  easily  learn  what  these  things  are. 
These  two  ways  of  studying  nature  are  called  observation 
and  experiment. 

Observation.  —  When  I  look  at  something  which  is 
going  on,  and  watch  carefully  to  see  what  happens,  my  act 
is  an  observation.  To  look  at  an  object  so  closely  that  we 
can  see  its  shape,  its  color,  and  whatever  else  is  visible 
about  it,  is  an  act  of  observation. 

If,  for  example,  I  desire  to  know  as  much  as  possible 
about  a  butterfly,  the  best  way  to  learn  it  is  to  catch  the 
butterfly,  look  at  it  intently,  note  down  and  remember 
what  I  see.  The  butterfly  would  show  me  that  it  has  four 
wings,  six  legs,  two  long  hair-like  bodies  (antennae)  reach- 
ing forward  from  its  head  with  knobs  upon  their  ends,  two 
large,  dark,  and  prominent  eyes  which  do  not  close  nor 
turn,  and  that  the  beautiful  colors  of  its  wings  are  due  to 
a  fine  dust  which  is  easily  rubbed  off  by  my  fingers.  All 
these  facts  I  could  learn  by  holding  the  insect  in  the  hand 
and  looking  at  it  thoughtfully. 

Knowledge  which  I  get  in  this  way  is  learned  by  obser- 
vation. 

9 


10 


OBSERVATION   AND    EXPERIMENT. 


Experiment.  —  But  if,  instead  of  only  looking  at  an 
object  as  I  find  it,  I  do  something  to  it  to  see  how  it  will 
behave  or  appear  in  different  conditions,  this  operation  is 
an  experiment. 

Will  5  cubic  centimeters  of  water  dissolve  as  much  as  10 
grams  of  granulated  sugar  ?  I  cannot  find  out  by  simply 
looking  at  sugar  and  water.  In  order  to  learn  what  the 
fact  is,  I  may  put  the  two  things  together  in  the  right 
way,  and  if  I  do  so  I  make  an  experiment.  Thus: 

Ex.  1.  —  I  take  a  tall  glass  cylinder,  a,  Fig.  1,  which  is 
graduated  to  measure  cubic  centimeters,  and  pour  in  water 


Fig.  1. 

up  to  the  5  cc.  mark.1  I  transfer  this  water  to  one  of 
the  thin  round-bottomed  cylinders,  b,  called  a  test-tube. 
I  also  weigh  out  10  g.  of  granulated  sugar2  and  put  it 
into  the  water  in  the  tube  b.8  I  now  warm  the  tube  in  the 
flume  of  a  Bunsen  lamp,  c.  There  is  danger  of  breaking 
the  tube  if  I  heat  it  too  suddenly,  or  too  long  in  one  spot, 

1  If  one  must  get  along  without  a  graduated  cylinder,  he  may 
obtain  5  cc.  very  nearly  by  filling  his  test-tube  one  inch  above  the 
rounded  bottom.  The  tube  is  supposed  to  be  £  inch  in  diameter. 

-  If  one  must  get  along  without  a  balance,  he  can  obtain  about 
10  g.  of  dry  sugar  by  filling  a  teaspoon  twice. 

8  Fold  a  narrow  strip  of  paper  into  the  shape  of  a  trough  and  lay 
this  in  the  tube,  which  should  be  held  in  a  slanting  position.  The  dry 
sugar  will  slide  safely  down  this  trough  .instead  of  clinging  to  the  wet 
walls  of  the  tube. 


OBSERVATION   ANJ)    EXPERIMENT.  11 

and  to  avoid  this  danger  I  move  it  slowly  in  the  flame  to 
heat  all  sides  evenly.  When  the  liquid  begins  to  boil  I  lift 
the  tube  into  the  hot  air  above  the  flame,  where  I  can  keep 
it  hot  without  boiling  it  too  vigorously.  I  watch  to  see 

Whether  the  sugar  remains,  or  becomes  less  and  less. 

Whether  it  all  finally  disappears. 

If  the  liquid  at  length  becomes,  as  it  will,  almost  or 
quite  transparent,  we  shall  know  that  5  cc.  of  hot  water  can 
dissolve  10  g.  of  sugar.  I  will  then  stand  the  tube  in  the 
tube-rack,  and  when  it  is  cold  I  will  look  again  and  see 

Whether  5  cc.  of  cold  water  can  hold  the  10  g.  in  solution. 

Let  us  keep  this  syrup  for  use  in  another  experiment. 

The  sap  of  some  trees  and  the  juices  of  some  plants  are 
natural  solutions  of  sugar  in  water,  but 
the  quantity  of  sugar  in  5  cc.  of  these 
juices  is  very  small.  Nothing  but  an 
experiment  could  have  first  shown  that 
5  cc.  of  water  can  dissolve  so  much 
sugar  as  we  have  found  it  to  do. 

But    in    experiments    we    often   put 
things   together  in  ways  in  which   na- 
ture never  does.     For  example,  I  wish 
to  know  how  sugar  will  behave  in  strong  sulphuric  acid. 
Nature  never  puts  these  two  things  together,  arid  the  only 
way  I  can  find  out  how  they  will  act  in  the  presence  of 
each  other  is  to  bring  them  together.     Thus: 

Ex.  2.  —  I  measure  out  5  cc.  of  strong  sulphuric  acid 
with  the  cylinder  a,  Fig.  1,  pour  it  into  an  empty  test-tube, 
then  rinse  the  cylinder  and  stand  it  on  a  small  plate,  Fig.  2. 
I  now  pour  the  sugar  syrup  made  in  the  other  experiment 
into  this  cylinder.  I  am  ready  now  to  bring  the  two  to- 
gether. I  pour  the  acid  in  a  slender  stream  into  the  syrup, 
and  watch  for  every  change  that  happens.  I  notice 

A  change  in  color. 

0?  TBM 


1-  o /•;>•£•/;  I  M770.Y   A  XI)    EXPERIMENT. 

A  change  in  volume  (size). 

A  change  in  temperature  (warmer  or  colder). 

A  new  substance  unlike  sugar  or  syrup  or  acid. 

As  soon  as  the  experiment  is  over  I  write,  in  my  note- 
book, a  short  account  of  what  I  did,  and  the  results  just  as 
I  saw  them. 

The  fact  is  that  a  coal-black,  bulky  mass  of  hot  carbon 
or  charcoal  is  the  result  of  bringing  these  two  substances 
together. 

,       The  science  of  Chemistry  is  founded  on  facts  which  have 
\  been  discovered  by  experiment,  and  the  most  natural  way 
j  to  study  Chemistry  is  by  the  same  means.    The  best  way  for 
tne  student  is  to  make  the  experiments  himself.     The  sec- 
ond best  way  is  to  see  them  made  by  a  teacher.     In  either 
case  the  student  should  remember  that  the  object  of  mak- 
ing experiments  is  to  discover  truth.     An  experiment  may 
be  pretty  and  interesting,  but  its  value  does  not  lie  in  its 
beauty.   "No  experiment  is  good  for  anything  in  the  study 
of  Chemistry  unless  it  helps  to  reveal  some  truth. 

The  student  should  reniember,  also,  that  it  is  not  what  he 
reads  about  experiments,  or  hears  a  teacher  say  about  them, 
that  is  going  to  give  him  the  best  and  quickest  insight  into 
Chemistry,  but  that  which  he  sees  with  his  own  eyes  and 
describes  in  his  own  words. 

To  study  Chemistry  by  experiment  the  student  should 
obey  the  following  rules  :  — 

1.  Arrange  the  apparatus  and  use  it  exactly  as  directed. 

2.  Watch  carefully  to  see  ever?/  change  which  takes  place. 

3.  Note  accurately  on  paper  every  Important  change. 

4.  Compare  these  results  with  the  facts  stated  in  the 
book,  and  correct  those  which  are  found  to  be  wrong. 

5.  Study  carefully  to  see  how  certain  inferences  may  be 
made  from  the  results. 


CHEMICAL    CHAXGES. 


WE  already  know  by  observation  that  there  are  changes 
ail  the  time  going  on  in  bodies  of  matter.  Some  things 
change  very  rapidly,  others  very  slowly.  Wood  changes 
to  smoke  and  ash  sometimes  in  a  few  minutes  ;  a  stone 
crumbles  to  powder  only  after  many  years.  But  nothing 
can  forever  stay  exactly  as  it  is. 

The  first  thing  we  have  to  do  in  Chemistry  is  to  become 
acquainted  with  these  changes.  How  do  they  differ  ?  How 
are  they  brought  about,  and  what  terms  are  used  to  de- 
scribe them  ? 

Ex.  3.  —  I   take  a  piece  of  magnesium  wire  or   ribbon       / 
about  six  inches  long,  grasp  one  end  with  a  pair  of  pincers,1 
and  hold  the  other  end  for  a  moment  in  the  flame  of  the 
Bunsen  lamp,  Fig.  3.     I  see  that 

The  metal  becomes  red  hot,  then  bursts  into  flame. 

Nothing  finally  remains  but  a  crumbling  white  solid. 

Ex.  4.  —  J  now  in 

the  same  way  hold  a 
piece  of  iron  wire  in 
the  flame  of  the  Bun- 
sen  lamp,  and  see  that 

The  metal  becomes  red  hot,  but 
does  not  burn. 

And  finally,  when  cold,  is  the 
same  substance  as  at  first. 

Both  metals  were  changed  by 
the  heat,  but  in  very  different 
ways.  The  iron  became  hot  in-  Fi  s 

1  A  homely  handle  can  be  made  by  starting  a  split  in  one  end  of  a 
stick.  The  wire  can  be  inserted  in  the  split  and  held  as  with  pincers. 

13 


14  CHEMICAL    C1IAX(,KS. 

stead  of  cold,  red  instead  of  black,  but  it  remained  iron. 
The  magnesium  did  not  remain  magnesium,  but  was  changed 
into  a  new  substance ;  the  crumbling  white  solid  is  a  very 
different  thing  from  the  tough,  gray,  and  lustrous  metal. 
There  was  no  change  in  the  substance  of  the  iron;  there 
was  a  change  in  the  substance  of  the  magnesium. 

Observations.  —  I  watch  the  clouds  and  see  them 
change  in  size  and  shape,  and  oftentimes  in  color.  But 
their  substance  does  not  change,  for  clouds  are  made  of 
water-vapor,  whatever  may  be  their  sizes,  shapes,  or  colors. 

To-day  a  piece  of  iron  is  smooth  and  bright,  but  if  left  in 
moist  air  it  will  in  time  be  found  covered  with  iron-rust. 

x 

A  part  of  the  iron  becomes  changed  into  this  very  different 

kind  of  matter. 

Further  observations  show  that  there  are  changes  going 
on  all  the  time  around  us  which  do  not  alter  the 
nature  of  substances,  like  the  changes  in  the  iron 
wire  when  heated.  All  such  changes  are  called 
physical  changes.  There  are  others  in  which 
the  substance  of  bodies  is  changed  into  matter 
of  a  different  kind,  like  the  burning  of  the 
magnesium.  All  such  changes  are  called  chem- 
ical changes .  And  so  we  learn  that  the  multi- 
"  *'  tudes  of  changes  in  the  world  of  matter  may  be 

grouped  in  two  great  classes. 

If  now  we  go  on  to  compare  one  chemical  change  with 
another  we  shall  find  that  there  are  several  different 
varieties. 

Decomposition.  Ex.  5.  —  I  put  one  gram  of  "  red  oxide 
of  mercury''  into  a  side-neck  ignition-tube,1  Fig.  4, —  just 

1  Ignition-tubes  are  made  of  "hard"  glass  while  other  tubes  are 
made  of  "  soft "  glass.  Hard  glass  will  stand  a  strong  heat,  while  soft 
glass  will  not.  Common  test-tubes  may  be  used  for  heating  liquids ; 
ignition-tubes  should  be  used  for  heating  dry  solids. 


CHEMICAL    CHANGES. 


15 


Fig.  6. 


about  enough  to  fill  the  rounded  bottom.    I  close  the  mouth 

of  the  tube  with  a  nicely  fitting  cork,  and  slip  one  end  of 

«ri  piece  of   rubber  tubing,  e,  Fig.  5,  over  the  end  of   the 

side-neck.     I  then  fix  the 

tube  very  obliquely  in  the 

clamp  of   the    support,  f. 

I  next  put  a  half-inch  of 

water  into  the  test-tube  £, 

and  slip  the  free  end  of  the 

rubber  tube  down  into  it. 

The  oxide  is  now  ready 
to  be  heated,  and  if  any- 
thing shall  be  driven  out 
we  may  catch  it  in  the 
test-tube. 

I  now  apply  the  flame  of  the  lamp,  and  move  it  slowly 
to  heat  the  bottom  of  the  tube  evenly.  The  upper  part  of 
the  tube  must  not  be  heated.  Now  look  for  and  describe 

A  change  in  the  color  of  the  oxide. 

A  coating  which  forms  on  the  cold  walls  of  the  tube. 

Bubbles  which  escape  from  the  rubber  pipe  in  the  water. 

A  change  in  the  quantity  of  the  oxide. 

Were  the  bubbles  which  came  over  through  the  water 
anything  more  than  air  ?  To  answer  this  question  I  take 
a  splinter  of  wood,  very  slender,  and  long  enough  to  reach 
to  the  bottom  of  the  tube,  set  fire  to  one  end  and  watch 
the  spark  very  closely  while  I  push  it  to  the  bottom  of  the 
tube  to  see 

Whether  it  burns  just  as  it  does  in  air. 

THE  FACTS.  —  By  heating  the  red  oxide  of  mercury  it  is 
first  blackened  and  then  broken  into  two  kinds  of  matter 
quite  unlike  itself.  One  of  these  appears  in  shining  drop- 
lets on  the  cold  walls  of  the  tube,  the  other  goes  off  as  a 


16  CHEMICAL    CHANGES. 

colorless  gas  which  brightens  the  burning  of  a  splinter. 
The  shining  droplets  which  coat  the  cold  walls  of  the  tube 
are  mercury,  and  the  gas  in  which  a  splinter  burns  with 
unusual  brightness  is  oxyyen. 

This  is  a  fine  example  of  chemical  change.  But  the  most 
important  thing  to  notice  is,  that  in  this  change  one  sub- 
stance is  broken  into  two  which  are  entirely  unlike  itself 
and  unlike  each  other.  Such  a  chemical  change  is  called 
deco  mpos  it  to  n . 

Decomposition  of  Potassium  Chlorate.  Ex.  6.  —  Po- 
tassium chlorate  is  a  white  solid.  Before  I  heat  it  the 
coarse  grains  or  crystals  should  be  reduced  to  powder:  I 
grind  it  in  a  mortar  (Fig.  6).  I  put  two 
grams  of  the  powder  into  the  ignition- 
tube,1  Fig.  4.  This  quantity  will  fill 
about  one  inch  of  the  tube.  I  put  three 
or  four  cubic  centimeters  of  blue  litmus 
6  solution  into  one  test-tube,  I,  and  as  much 

lime-water  into  a  second  tube,  c,  Fig.  5, 
and  provide  a  good  cork  for  each.  I  put  the  end  of  the 
rubber  tube  into  the  litmus,  and  then  heat  the  chlorate  just 
as  I  did  the  red  oxide  before.  Watch  for  and  describe 

The  changes  in  the  chlorate. 

The  bubbles  from  the  pipe  in  the  litmus. 

After  a  while  I  put  a  match-flame  into  the  mouth  of 
the  tube  and  see  that  it  burns  with  unusual  brightness. 
This  shows  that  the  tube  is  filled  with  oxygen. 

I  then  put  the  end  of  the  rubber  tube  over  into  the  lime- 
water  in  c,  and  close  b  with  its  cork,  in  order  to  keep  its 
oxygen  for  use  further  on. 

At  length  the  boiling  chlorate  thickens,  and  soon  after 

1  The  tube  must  be  clean  and  dry.  A  piece  of  dry  cloth,  or  a  sponge 
tied  on  the  end  of  a  wire  or  stick,  is  convenient  for  wiping  tubes. 


CHEMICAL    CHANGES.  17 

dries  up  completely  to  a  white  solid.  The  work  is  done. 
I  stop  the  heat,  remove  the  rubber  tube,  and  cork  the  test- 
tube  c,  to  keep  its  oxygen  also  for  future  use. 

Has  any  change  been  made  in  the  litmus  or  the  lime 
water  ? 

THE  FACTS.  —  By  heating  potassium  chlorate  it  is  first 
melted  and  afterward  broken  into  two  substances,  unlike 
itself  and  each  other.  One  is  the  white  solid,  left  in  the 
ignition-tube,  and  the  other  is  oxygen.  The  chlorate  is 
decomposed. 

Oxygen,  which  has  appeared  in  both  these  experiments, 
is  an  important  substance,  and  as  soon  as  we  are  through 
with  the  special  study  of  chemical  changes  we  will  examine 
it  fully.  At  present  we  will  make  two  experiments  with  it. 

Combination.  —  What  will  happen  if  a  bit  of  coal  is 
heated  in  oxygen  ? 

Ex.  7.  —  I  wind  the  end  of  a  small  wire  around  a  little 
splinter  of  charcoal,  heat  the  charcoal  until  it  holds  a  spark 
of  fire,  and  then  lower  it  into  the  oxygen  in  the  test-tube  c, 
Fig.  5,  over  lime-water.  Notice  » 

What  effect  is  produced  on  the  spark. 

Whether  the  charcoal  wastes  away. 

Wrill  the  oxygen  brighten  a  match-flame  afterwards  ? 

I  now  cover  the  mouth  of  the  tube  with  my  finger  anJ 
shake  it  briskly. 

What  change  takes  place  in  the  lime-water  ? 

THE  FACTS.  —  Charcoal  with  a  dull  red  spark  will  glow 
brightly  in  oxygen  and  burn  away  rapidly ;  the  oxygen  is 
used  up  at  the  same  time,  and  the  lime-water  afterward 
becomes  turbid  and  white. 

But  we  know  that  oxygen  will  not  whiten  lime-water : 
this  was  proved  in  Ex.  6.  (How  was  it  proved  ?)  Charcoal 
also  will  not  whiten  lime-water.  But  the  burning  of  the 


18  CHEMICAL    CHANGES. 

charcoal  in  oxygen  yields  something  which  will.     It  is  a  col- 
orless gas  called  carbon  dioxide.     In  place  of  charcoal  and 
oxygen  we  have  carbon  dioxide,  which  is  very  unlike  both. 
Now  the  thing  most  important  to  see  in  this  case  is  that 
two  substances  are  changed  into  one. 

Ex.  8.  —  I  take  a  piece  of  wire,  —  perhaps  a  knitting- 
needle,  —  warm  it  a  little,  and  then  plunge  it  into  some 
flowers  of  sulphur.  A  thin  layer  of  sulphur  will  cling  to 
the  wire.  I  set  fire  to  this  sulphur,  and  then  at  once  thrust 
it  into  the  test-tube  b,  containing  oxygen  and  litmus,  left 
from  Ex.  (>.  Notice  and  describe 

The  fine  color  of  the  flame. 

The  vapor  which  is  produced. 

I  next  close  the  tube  with  my  finger  and  shake  it  to  mix 
the  vapor  with  the  litmus. 

What  change  is  made  in  the  color  of  the  litmus  ? 

Sulphur  burns  more  freely  in  oxygen  than  in  air,  and 
with  a  rich  blue  flame,  filling  the  vessel  with  white  vapor. 
This  vapor  mixed  with  blue  litmus  solution  changes  the 
color  from  blue  to  red.  In  place  of  the  sulphur  and  oxy- 
gen, both  of  which  are  used  up,  we  have  a  new  substance 
quite  different  from  either.  This  new  substance  into  which 
sulphur  and  oxygen  are  changed  is  called  sulphur  dioxide. 

Now  this  change  is  like  the  change  when  the  charcoal 
was  burned.  It  is  another  case  in  which  two  substances  are 
changed  into  one.  Such  a  chemical  change  is  called  combi- 
nation. 

Decomposition  or  Combination?  —  When  ammonia 
and  hydrochloric  acid  are  mixed  a  chemical  change  occurs ; 
is  it  a  chemical  decomposition  or  a  chemical  combination  '.' 

Ex.  9.  —  I  put  a  cubic  centimeter  of  strong  ammonia 
water  into  a  tube  or  bottle,  rinse  it  around  to  wet  the  sides, 
and  then  pour  it  out.  I  put  as  much  hydrochloric  acid  into 


CHEMICAL    CHANGES.  19 

another  similar  vessel  and  treat  it  in  the  same  way.  By 
this  means  I  fill  the  vessels  with  the  colorless  vapor  of  the 
two  substances.  I  next  bring  these  two  vessels 
mouth  to  mouth  and  hold  them  one  above  the  other 
(Fig.  7).  Notice  and  describe 

The  change  which  the  colorless  vapors  undergo. 
The  two  substances  used  are  colorless,  but  a  new 
one  is  made  which  is  seen  as  a  white  cloudlike  mass, 
which  rolls  down  toward  the  bottom  of  the  tube, 
and  will  roll  back  again  if  the  tubes  be  inverted. 
In  fact,  the  hydrochloric  acid  and  ammonia  com- 
bine to  form  one  thing,  —  called  ammonium  chloride.  Fi«- 7- 

Substitution.  —  All  chemical  changes  are  either  decom- 
positions or  combinations.  But  in  a  great  many  cases  the 
two  kinds  take  place  at  once.  This  is  true  in  the  action  of 
zinc  and  hydrochloric  acid. 

Ex.  10.  —  I  have  a  wide-mouth  bottle  which 
will  hold  200  cc.  and  a  square  of  glass  or  of 
heavy  paper  with  which  to  cover  it. 

Into  the  bottle  I  put  two  or  three  pieces  of 
zinc,  and  just  cover  them  with  hydrochloric  acid. 
I  then  close  the  bottle  with  its  cap  of  glass  or 
paper  (Fig.  8). 
Describe  the  action  which  sets  in. 
Feel  the  bottle,  and  what  effect  is  discovered  ? 
I  now  bring  a  match-flame  to  the  mouth  of  the  bottle 
while  I  lift  the  cover. 
Describe  the  result. 

A  violent  effervescence  takes  place  whenever  zinc  and 
hydrochloric  acid  are  brought  together.  The  vessel  is 
heated,  and  a  gas  escapes  which  takes  fire  with  explosion. 
This  gas  is  hydrogen.  Heat  and  hydrogen  are  two  products 
of  the  chemical  action.  Are  there  any  others  ? 


CHEMICAL    CHANGES. 


a 


V 


Fig.  9. 


Ex.  11.  —  To  answer  this  question  I  examine  the  liquid 
left  in  the  bottle,  when  the  bubbling  of  gas  has  come  to  an 
end.  I  must  first  filter  the  liquid  to  rid  it  of  black  flakes, 
which  are  only  impurities  of  the  zinc,  and  afterward 
evaporate  the  liquid  to  recover  any  solid  substance  it  may 
contain. 

1.  Filtration.  —  Cut  a  square  of  filter  paper,  A,  Fig.  9, 
about  three  inches  on  a  side,  —  a  little  less  than  twice  the 

length  of  the  sloping  side  of 
a  funnel,  /.  Fold  the  square 
into  a  triangle  by  bringing 
corners  d  and  a  together. 
Fold  again,  bringing  corners 
c  and  b  together,  making  the 
triangle  B. 

Then  trim  the  edges  along 
the  circular  line  e  h.     Open 

the  triangle  (leaving  three  thicknesses  of  paper  on  one  side 

and  one  on  the  other),  and  we  have  a  little 

paper  funnel,   C,  which  will  fit  neatly  in 

the  glass  funnel,  /.     Press  it  in  and  wet 

it  with  water.     Then  rest  the  funnel  on  a 

test-tube  and  pour  the  liquid  with  its  sedi- 
ment into  it.     The  liquid  will  run  through, 

but  the  sediment  will  stay  on  the  filter. 

2.  Evaporation.  —  Pour   the    clear 
liquid  into  a  porcelain  dish  and  heat 
it  over  a  low  flame,  as  shown  in  Fig. 
10.     It  may  boil,  but  should  do  so 
very  gently.     The  water  will  slowly 

pass  away  as  vapor,  but  any  solid  substance  which  is  dis- 
solved in  it  will  stay  in  the  dish. 

I  will  evaporate  the  liquid  left  in  Ex.  10,  and  just  fil- 
tered, down  to  about  one-third  its  bulk,  and  then  let  it 


Fig.  10. 


CHEMICAL    CHANGE*.  21 

stand  until  it  is  cold.  A  brown  solid  is  now  seen,  if  the 
evaporation  has  gone  far  enough.  This  brown  solid  must 
have  been  made  by  the  action  of  the  zinc  on  the  hydro- 
chloric acid  in  Ex.  10.  It  is  called  zinc  chloride. 

We  began  the  experiment  with  zinc  and  acid ;  we  after- 
wards find  hydrogen,  the  brown  solid,  and  heat,  in  place  of 
these  twt)  substances. 

In  all,  we  have  now  found  three  products  of  the  chemical 
action  of  zinc  and  hydrochloric  acid.  They  are  heat,  hydro- 
gen, and  zinc  chloride. 

Now  hydrochloric  acid  is  a  compound  of  the  two  ele- 
ments hydrogen  and  chlorine,  and  the  zinc  just  takes  the 
place  of  the  hydrogen  in  it.  In  fact,  the  zinc  has  decom- 
posed the  hydrochloric  acid  and  combined  with  the  chlorine 
of  that  substance.  The  hydrogen  was  driven  out  as  a  gas, 
which  burned  quickly  while  the  solid  zinc  chloride1  stayed 
behind  in  solution. 

When  one  substance  takes  the  place  of  another  in  a  com- 
pound, as  the  zinc  took  the  place  of  hydrogen  in  the  acid, 
the  action  is  called  substitution.  This  is  one  of  the  most 
common  kinds  of  chemical  action. 

Double  Decomposition.  —  It  often  happens  that  when 
two  things  are  brought  together  both  are  decomposed.  This 
is  the  case  with  silver  nitrate  and  sodium  chloride. 

Ex.  12.  —  I  take  a  small  crystal  of  silver  nitrate  and  drop 
it  into  a  test-tube  with  5  cc.  of  water,  and  shake  it  until  it 
is  dissolved.  In  another  test-tube  I  dissolve  some  common 
salt,  which  in  chemistry  is  known  as  sodium  chloride.  I 
now  add  a  drop  or  two  of  the  solution  of  salt  to  the  silver 
nitrate.  After  seeing, 

What  happens  to  show  that  a  chemical  action  occurs  ? 
I  go  on  adding  the  solution  of  salt  carefully,  drop  by  drop, 

1  The  solid  is  called  zinc  chloride  because  it  is  made  up  of  zinc  and 
chlorine.  When  pure  it  u  nearly  white. 


CHEMICAL    CHANGES. 

watching  to  see  whether  still  more  of  the  new  substance  is 
made  by  each  addition;  and  that  I  may  make  no  mistake 
about  this  I  shake  the  tube  each  time  vigorously,  and  then 
wait  till  the  solid  settles  a  little  before  I  add  the  next 
drops.  I  do  this  until  a  drop  of  the  liquid  gives  no  more 
of  the  white  solid,  and  stop  with  that  drop. 

If  by  accident  I  do  get  in  a  drop  more  than  thte,  I  add  a 
drop  of  silver  nitrate  solution. 

I  then  filter  the  mixture  as  in  Ex.  11.  The  white  solid 
will  be  left  on  the  filter-paper  while  a  clear  liquid  will  run 
through. 

I  next  evaporate  this  clear  liquid,  as  shown  in  Fig.  10, 
until  but  little  is  left,  and  then,  when  it  cools,  crystals 
will  appear.  The  new  white  solid  is  silver  chloride,  and 
the  crystals  are  sodium  nitrate. 

The  silver  nitrate  and  sodium  chloride  decompose  each 
other,  and  then  the  silver  and  sodium  just  change  places 
and  form  the  two  new  compounds  named  above.  The 
names  themselves  show  this  double  change,  thus :  silver 
nitrate  and  sodium  chloride  become  sodium  nitrate  and 
silver  chloride. 

In  all  such  cases  as  this,  in  which  two  substances  decom- 
pose one  another  and  form  two  new  ones,  the  action  is 
called  double  decomposition.  We  shall  find  another  exam- 
ple of  double  decomposition  in  the  action  of  mercuric 
chloride  and  potassium  iodide. 

Ex.  18.  —  I  take  enough  mercuric  chloride  in  powder 
to  half-way  fill  the  rounded  bottom  of  a  test-tube,  cover 
it  with  5  cc.  of  water,  and  warm  it  until  it  is  dissolved. 
I  take  about  twice  as  much  potassium  iodide  in  another 
tube  and  dissolve  it  also  in  water.  I  put  about  JoO  cc. 
of  water  into  a  wide-mouth  bottle,  and  add  the  mercuric 
chloride  solution.  I  now  put  in  about  one-half  the  solu- 
tion of  potassium  iodide,  little  by  little. 


CHEMICAL    CHANGES.  23 

Describe  the  result  as  it  first  appears. 
And  the  curious  change  which  soon  occurs. 

I  go  on  adding  the  iodide,  carefully  noticing  whether  still 
more  of  the  new  substance  is  made  by  each  addition,  and, 
that  I  need  make  no  mistake,  I  wait  each  time  to  let  the 
solid  settle  a  little  and  the  liquid  clear  before  I  add  the 
next  drops.  I  do  this  until  a  drop  of  the  iodide  gives  no 
more  of  the  colored  solid,  and  stop  with  that  drop.  If  by 
accident  I  do  get  in  too  much,  I  will  add  drops  of  mercuric 
chloride  until  the  last  drop  has  no  effect.  The  scarlet  solid 
will  soon  settle  and  leave  a  clear  liquid  above  it. 

We  find  that  when  mercuric  chloride  and  potassium 
iodide  are  brought  together  in  solution  they  yield  a  sub- 
stance whose  color,  at  first  bright  yellow,  very  soon  changes 
to  a  fine  scarlet.  The  potassium  iodide  will  give  this  sub- 
stance just  as  long  as  there  is  any  mercuric  chloride  in  the 
solution.  When  a  drop  fails,  we  may  know  that  the  chlo- 
ride is  all  used  up.  The  scarlet  precipitate  (as  we  call  a 
solid  which  comes  by  putting  two  liquids  together)  and 
a  solid  substance  which  stays  dissolved  in  the  water  are 
the  two  new  things  into  which  the  chloride  and  iodide 
were  changed. 

Now  the  chemists  tell  us  that  mercuric  chloride  contains 
mercury  and  chlorine,  and  that  potassium  iodide  contains 
potassium  and  iodine.  When  we  put  these  two  liquids  to- 
gether the  chlorine  and  iodine  changed  places.  Our  scar- 
let solid  contains  the  mercury  and  iodine,  and  our  white 
solid  contains  the  potassium  and  chlorine.  In  fact,  loth  of 
the  old  substances  were  decomposed,  and  the  two  new  ones 
were  made  by  their  parts  combining  in  different  pairs. 

SUGGESTION  TO  THE  STUDENT. — Notice  all  along  how  the 
name  of  a  substance  tells  us  also  the  names  of  the  simpler  sub- 
stances in  it.  When  we  see  the  name  mercuric  chloride  we  may 
be  reminded  of  the  names  of  its  parts,  mercury  and  chlorine ;  and 


24  CHEMICAL    CHANGES. 

in  the  same  way  potassium  iodide  suggests  its  parts,  potassium 
and  iodine.  So,  too,  our  yellow  solid  made  of  mercury  and  iodine 
is  named  mercuric  iodide. 

Definitions.  —  A  substance  which  is  made  up  of  two  or 
more  kinds  of  matter  quite  unlike  itself  is  called  a  com- 
2)ound.  Mercuric  oxide  is  a  compound  of  mercury  and 
oxygen.  For  the  proof  of  this  see  Ex.  5. 

The  different  kinds  of  matter  of  which  a  substance  is 
made  are  called  its  constituents.  Mercury  and  oxygen  are 
the  constituents  of  mercuric  oxide  ;  sulphur  and  oxygen,  of 
sulphur  dioxide  (Ex.  8). 

By  far  the  larger  number  of  substances  are  compounds ; 
but  there  are  a  few  which  have  never  yet  been  decomposed, 
and  such  are  called  elements.  Mercury,  oxygen,  and  sul- 
phur are  examples  of  elements.  Some  seventy  of  these 
are  now  known,  and  out  of  this  small  number  all  the  com- 
pounds in  nature  are  made. 

But  compounds  rarely  occur  pure.  Substances  are  min- 
gled together  two  or  more  so  completely  that  they  seem 
to  be  only  one,  and  yet  each  still  has  all  its  properties 
unchanged.  Syrup  of  sugar  is  an  example.  The  sugar  and 
the  water  are  simply  mixed  together  without  change  of 
properties.  Such  substances  are  called  mixtures.  Brine  is 
another  example. 

All  substances  are  either  elements,  compounds,  or  mix- 
tures. 

There  are  two  ways  of  finding  out  what  the  constituents 
of  a  compound  are ;  one  is  analysis,  the  other  synthesis. 
Any  process  in  which  we  decompose  a  substance  so  as  to 
learn  what  it  is  made  of  is  an  analysis.  Ex.  5  was  an 
analysis  of  mercuric  oxide.  Any  process  in  which  we 
make  a  compound  by  putting  its  constituents  together  is  a 
synthesis.  Ex.  8  was  a  synthesis  .of  sulphur  dioxide,  and 
in  Ex.  7  we  found  that  carbon  dioxide  is  composed  of  car- 


CHEMICAL    CHANGES.  25 

bon  and  oxygen  by  making  these  two  elements  combine. 
This  also  was  an  example  of  synthesis. 

Heat  and  Chemical  Action Heat  is  very  often  pro- 
duced by  chemical  changes.  It  was  so  in  Ex.  10.  It  is  so, 
for  another  example,  in  the  case  of 

SULPHURIC  ACID  AND  WATER.  —  Ex.  14-  Into  a  wide- 
mouth  bottle  I  pour  40  cc.  of  cold  water,  and  provide  a  rod 
of  glass,  or  of  wood,  with  which  to  stir  it.  I  then  pour  into 
it  gradually,  while  I  stir  it,  40  cc.  of  strong  sulphuric  acid.1 
Note  the  evidence  that  heat  is  produced  as  shown 

By  handling  the  bottle. 

By  inserting  a  test-tube  holding  a  little  alcohol. 

These  chemical  changes  need  no  extra  heat  to  start  them, 
but  yield  heat  as  one  of  the  products  of  the  action. 

There  are  other  cases  in  which  heat  must  be  used  to  start 
the  change  (Ex.  7  and  Ex.  8),  which  once  started  produces 
heat  enough,  and  often  more  than  enough,  to  keep  the 
action  going.  We  touch  the  wood  with  a  match-flame  to 
start  a  fire,  but  once  begun  the  burning  is  kept  up  by  the 
heat  of  the  chemical  action  itself. 

There  are  still  other  cases  in  which  heat  must  be  applied, 
not  only  to  start  the  action,  but  also  to  keep  it  going  (Ex.  5 
and  Ex.  6).  In  these  cases  heat  is  not  produced,  but  ab- 
sorbed, by  the  chemical  action. 

The  fact  is  that  every  chemical  action  is  a  source  of  heat 
or  cold ;  every  change  in  the  nature  of  a  substance  is  accom- 
panied by  a  change  in  temperature. 

Electricity  and  Chemical  Action.  —  We  are  told  in 
the  study  of  Pliysics,  that  if  a  strip  of  amalgamated  zinc 
and  another  of  copper  are  put  into  a  vessel  of  very  dilute 
acid  they  will  yield  a  current  of  electricity. 

1  The  heat  would  be  stronger  if  the  water  were  poured  into  the  acid. 
This  should  never  be  done.  Whenever  strong  sulphuric  acid  and  water 
are  to  be  mixed  always  pour  the  acid  gradually  into  the  water  while 
von  stir  it. 


26  CHEMICAL    CHANGES. 

Ex.  15.  —  I  first  make  a  little  zinc-copper  couple  in  this 
way :  I  cut  from  a  sheet  of  zinc,  such  as  is  used  under 
stoves,  a  strip  four  inches  long  by  one-half  inch  in  width 
and  bend  it  squarely  at  three-fourths  inch  from  one  end,  ,v, 
Fig.  11.  I  then  amalgamate  it.  For  this  I  take  a  few 
cubic  centimeters  of  the  half-strong  acid  which  was  made 

in  Ex.  14,  and  add  to 
it  five  times  as  much 
water  in  a  saucer.  I 
must  also  have  a  little 
mercury  in  a  test-tube. 
I  first  wet  the  zinc 
with  the  acid.  I  next 
pour  the  mercury  first 
upon  one  side,  then  upon  the  other,  and  rub  the  whole  sur- 
face gently  with  a  piece  of  cloth.  The  surface  of  the  zinc 
should  now  shine  like  silver ;  it  is  amalgamated. 

I  next  take  a  piece  of  sheet-copper  as  wide  as  the  zinc 
and  two  and  a  half  inches  long,  and  fold  one  end,  as  shown 
at  c.  I  press  the  end  of  z  into  this  fold  and  make  the  two 
fit  closely  by  pressing  the  fold  carefully  (not  to  break  the 
zinc)  with  pincers.  The  upright  part  of  c  is  about  two 
inches  long  and  stands  facing  the  upright  part  of  2,  as 
shown  at  a,  Fig.  11. 

To  prepare  the  dilute  acid :  I  measure  into  the  water-pan 
p  water  enough  to  be  a  little  deeper  than  the  copper  c  is 
high,  and  then  add  one-twentieth  as  much  strong  sulphuric 
acid. 

I  shall  also  need  a  test-tube :  to  have  it  ready  I  lay  one 
in  the  water,  let  it  fill  and  sink. 

These  preparations  all  made,  I  next  stand  the  zinc-copper 
in  the  acid  water. 

A  torrent  of  bubbles  rise  alongside  the  copper.  AY  hut 
are  these  bubbles  ?  To  catch  them  I  lift  the  test-tul>e, 


CHEMICAL    CHANGES.  27 

bottom  upward,  letting  no  air  enter  it,  and  bring  its  mouth 
over  the  top  of  the  copper,  as  shown  at  b.  The  bubbles 
now  rise  into  the  tube,  driving  the  water  out  at  the  rate  of 
1  cc.  a  minute,  if  everything  works  well.  When  the  tube  is 
about  half  filled  with  gas  I  light  a  match,  and  lift  the  tube 
slowly ;  the  water  falls  out,  air  takes  its  place,  and  as  the 
flame  touches  the  mouth  of  the  tube  a  sharp  report  occurs, 
which  says  —  hydrogen  ! 

The  acid  water  is  decomposed  and  hydrogen,  is  set  free. 
But  amalgamated  zinc  alone  will  not  decompose  the  acid 
(try  it),  nor  will  copper  alone  (try  it).  Is  there  anything, 
more  than  zinc  and  copper,  when  they  are  together  in  the 
acid?  Yes,  there  is,  as  we  are  told,  the  current  of  elec- 
tricity. The  zinc-copper  is  a  source  of  electricity,  and  the 
hydrogen  is  set  free  by  the  action  of  electricity. 

It  is  found  that  a  great  many  chemical  changes  can  be 
made  by  means  of  electricity.  And,  on  the  other  hand,  a 
great  many  chemical  changes  produce  electricity.  Like 
heat,  electricity  is  sometimes  an  agent  and  sometimes  a 
product  in  chemical  action. 

Light  and  Chemical  Action Light  is  also  a  product 

of  chemical  action.  The  light  of  our  fires  and  the  light  of 
our  oil  and  gas  lamps  are  examples.  Remember,  also,  the 
burning  of  sulphur  in  Ex.  8,  and  of  charcoal  in  Ex.  7. 

Light  will  also  sometimes  produce  chemical  changes. 

Ex.  16.  —  I  first  make  some  silver  chloride  by  filling 
a  test-tube  three-fourths  full  of  water,  adding  a  small  crys- 
tal of  silver  nitrate,  shaking  until  the  crystal  is  dissolved, 
and  then  adding  hydrochloric  acid  drop  by  drop.  The  white 
cloud  which  rolls  down  is  silver  chloride.  I  now  place  the 
tube  in  strong  sunlight. 

What  change  occurs  in  the  color  of  the  chloride  ? 
The  change  in  color  slowly  from  white  to  dark  purple  is 


CHEMICAL    CHANGES. 

a  sign  that  a  new  substance  is  being  made.  In  fact,  light 
decomposes  the  silver  chkride.  For  other  examples,  and 
for  the  explanation  of  this  one,  we  must  wait. 

Heat,  light,  and  electricity  are  agents  which  we  can  use 
to  bring  about  chemical  actions  which  in  their  absence  will 
not  occur. 

Heat,  light,  and  electricity  are  also  products  of  chemical 
action.  They  are  just  as  important  to  the  chemist  as  are 
the  material  products,  that  is,  the  new  substances,  obtained 
at  the  same  time. 

We  now  go  on  to  examine  hydrogen  and  oxygen  gases 
which  we  have  met  with  in  several  experiments. 

HYDROGEN. 

Hydrogen  may  be  made  by  zinc  and  hydrochloric  acid,  as 
it  was  in  Ex.  10.  We  may  make  and  catch  it  as  follows : 

Ex.  17.  —  I  make  enough  dilute  hydrochloric  acid  —  one 
measure   of    strong    acid    to   two 
measures    of    water  —  to  fill    the 
-.^^^g         water-pan  about  two  inches  deep. 
I  take  the  graduated  cylinder,  lay 
Fig-12-  it  in  the  acid,  as  shown  in  Fig.  12, 

and  when  it  is  thus  filled  with  the  liquid  I  lift  it  bottom 
upward  and  let  it  stand  mouth  down 
on  the  bottom  of  the  pan,  as  in  Fig. 
13.  I  next  drop  a  piece  of  granu- 
lated zinc  into  the  pan,  and  then 
carry  the  mouth  of  the  cylinder  over 
it.  In  all  this  work  I  use  great  care 
to  not  let  a  bubble  of  air  get  into 
the  cylinder.  The  hydrogen  bubbles 
form  on  the  zinc,  rise  in  the  cylin-  ~  Fig.  is. 

der,  and  push  the  water  down  out 'of  it,  as  shown  in  Fig.  14, 
until  finally  the  cylinder  is  filled  with  hydrogen. 


CHEMICAL    CHANGES. 


20 


To   Discover  the  Properties  of   Hydrogen 1  test 

the  gas  by  lighting  a  match,  then  lifting  the  cylinder  out 

of  the  liquid  rather  slowly,  mouth 

still  downward,  and  then   quickly 

bringing  the    flame    to    the    open 

mouth.     The  gas  takes  fire  with  a 

dull  report.     Compare   this   result 

with  that  in  Ex.  10. 

Ex.  18.  —  I  fill  the  cylinder  again 
with  the  gas,  and  lift  it  from  the  rig. 

water  in  the  same  way,  then  turn  it  over  and  let  it  stand 
on  the  table  open  while  I  light  a  match.    I  bring  the  match 
to  the  mouth  of  the  jar. 
Why  is  there  no  report  ? 
Which  is  heavier,  hydrogen  or  air  ? 
What  is  the  color  of  hydrogen  ? 

Ex.  19.  —  I  put  30  cc.  of  water  into  the  mortar,  Fig.  6,  and 
30  cc.  strong  hydrochloric  acid.  I  drop  into  this  a  piece  of 
zinc,  and  then  place  a  small  funnel,  mouth  down,  over  the 
zinc.  I  next  bring  the  mouth  of  a  test-tube 
down  over  the  stem  of  the  funnel,  as  shown 
in  Fig.  15.  The  action  should  be  brisk ;  and 
if  it  be  so,  then,  after  one  minute,  I  slowly 
lift  the  tube  —  keeping  its  bottom  up  — 
carry  it  away  from  the  stem,  and  then  bring 
a  lighted  match  to  its  mouth.  A  dull  explo- 
sion proves  that  the  tube  is  full  of  hydrogen. 
The  hydrogen  rises  through  the  air  to  the 
top  of  the  tube,  collects  there  and  gradually 
pushes  the  air  down  and  out  at  the  bottom.  If  the  explo- 
sion is  sharp,  it  shows  that  the  tube  was  only  partly  filled. 
Then  repeat  the  experiment,  and  wait  longer. 

Other  gases  which  are  lighter  than  air  may  be  collected 
by  this  method,  called  upward  displacement.    Oxygen,  which 


Fig.  15. 


30  CHEMICAL    CHANGES. 

is  Tieavier  than  air,  is  collected  (Fig.  5)  by  downward  dis- 
placement. In  Ex.  17  the  gas  was  collected  by  displace- 
ment of  water  instead  of  air,  and  this  method  may  be  used, 
whether  the  gas  is  lighter  or  heavier  than  air. 

WHAT  CAUSES  THE  EXPLOSION?    Ex.  20.  —  I  take  a  short 
piece  of  glass  tube,  which  is  drawn  out  to  a  small  jet  at  01  it- 
end,  and  fix  it  with  a  piece  of  rubber  tubing 
upon  the  stem  of  the  funnel.     I  again  put 
dilute  hydrochloric  acid  in  the  mortar,  add 
the  zinc,  and  place  the  funnel  over  it.     The 
gas  must  come  off  very  briskly ;  and,  if  need 
be  to  make  it  do  so,  I  add  more  strong  acid. 
After  about  half  a  minute,  if -the  gas  is  com- 
ing fast,  and  longer  if  not,  so  that  the   air 
Fig.  IB.         shall  be  all  driven  out,  I  bring  a  match-flame 
to  the  top  of  the  jet  on  the  end  of  the  funnel.     The  gas 
takes  fire  with  the  usual  dull  explosion,  but  goes  on  burn- 
ing as  quietly  as  a  candle.     Fig.  16  shows  this  result. 
Then  is  hydrogen  itself  explosive  ? 
Note  also  if  the  flame  is  pale  or  brilliant.      — , 
Is  it  a  hot  flame  ?     Try  it  with  a  small  wire. 
7£r.  21. — But   what   causes   the  explosion,  if  hydrogen 
can   burn   without   it  ?     I  will   collect   a  little   hydrogen 
over  water,  as  in  Ex.  17.     But,  instead  of  filling  the  cylin- 
der with  the  liquid,  I  will  leave  it  about  two-thirds  full  of 
air,  filling  only  about  one-third  its  height  with  the  water. 
The  liquid  will  soon  be  driven  out,  and  then  the  cylinder 
is  filled  with  a  mixture  of  hydrogen  and  air.     I  now  lift  it 
from  the  pan,  and  at  once  bring  a  match-flame  below  its 
mouth.     A  sharp  explosion  follows. 

What  substances  together  explode  in  this  case  ? 
Have  these  same  ones  been  together  before  whenever  the 
explosion  has  occurred  ? 

What,  then,  is  the  material  which  explodes? 


CHEMICAL    CHANGES. 


31 


What  new  Substance  made  by  burning  Hydrogen? 
Ex.  22.  —  To  answer  this  question  I  must  burn  pure  dry 
hydrogen  and  catch  the  products.  I  will  make  the  hydro- 
gen as  in  Ex.  20,  but  before  I  light  the  jet  I  must  dry  the 
gas,  and  I  can  do  this  by  passing  it  over  calcium  chloride, 
which  absorbs  water  greedily. 

I  take  a  "drying-tube,"  a,  Fig.  17,  put  a  little  cotton- 
wool in  the  bulb  loosely,  drop  in  small  pieces  of  calcium 
chloride  to  fill  the  tube  nearly  full,  and  put  a  thin  layer  of 
cotton  over  it.  I  next  close  the  large  end  with  a  cork  hav- 
ing a  hole,1  through  which  I  crowd  the  end  of  the  stem  of 
the  funnel,  b,  Fig.  17. 

I  now  put  several  frag- 
ments of  the  zinc  into  the 
mortal' ;  afterward  place 
the  funnel  over  the  zinc 
and  fix  the  drying-tube 
firmly  in  the  clamp  of  the 
support  s,  as  shown  in 
Fig.  17.  This  done,  I 
pour  dilute  hydrochloric 
acid  into  the  mortar. 

Hydrogen  is  set  free. 
It  goes  up  through  the 
calcium  chloride,  which 
takes  out  the  water. 
The  dry  hydrogen  escapes  from  the  jet  above. 

After  waiting  until  I  am  sure  that  the  air  is  all  driven 
out,  I  set  fire  to  the  dry  hydrogen  at  the  top  of  the  tube, 
and  then  I  hold  a  glass  tumbler,  or  a  wide-mouth  bottle, 
which  is  clean  and  dry,  over  the  flame,  as  shown  at  c. 

1  Holes  are  made  through  corks  by  means  of  "  cork-borers,"  made 
for  the  purpose.  They  may  also  be  easily  made  by  first  running  a  hot 
pointed  wire  through  the  cork,  and  then  using  a  round  file  to  enlarge 
the  hole.  Each  hole  should  be  made  to  fit  its  tube  very  closely. 


Fig.  17 


CHEMICAL    CHANCES. 

Notice  a  deposit  of  dew  on  the  Avails  of  the  bottle;  it  is 
nothing  but  water.  This  is  the  substance  made  by  burn- 
ing hydrogen  in  air. 

What  are  two  other  products  ?     See  p.  28. 

Description  of  Hydrogen.  —  We  have  found  that  hy- 
drogen is  a  gas  without  color,  and  when  pure  it  is  also 
without  odor  and  taste.  It  is  very  much  lighter  than  air 
(Exs.  18  and  19).  An  equal  bulk  of  air  is  14.44  times 
heavier  than  this  gas.  In  fact,  hydrogen  is  the  lightest 
of  known  substances.1 

Hydrogen  unmixed  with  air  burns  with  a  silent  flame 
(Ex.  20),  but  when  mixed  with  air  the  mixture  burns  with 
explosion  (Ex.  21).  The  chemical  action  is  the  same  in 
both  cases :  water,  heat,  and  light  are  the  products  of  this 
action  (Ex.  22).  There  is  nothing  in  this  experiment  to 
show  what  the  hydrogen  combines  with  to  make  the  water. 
Let  us  remember  this. 

The  flame  of  burning  hydrogen  is  very  hot  (Ex.  20).  In 
fact,  no  other  fuel  gives  so  hot  a  fire  as  this.  One  gram  of 
this  gas  will  yield  enough  heat  in  burning  to  boil  344.62  g. 
of  ice-cold  water. 

A  unit  of  heat  is  so  much  heat  as  will  raise  the  tem- 
perature of  1  g.  pure  water  1°  C.  This  unit  is  called  a 
calorie,  just  as  the  unit  of  weight  is  called  a  grant.  The 
heat  of  all  chemical  changes  is  measured  by  this  unit. 
The  burning  of  the  gram  of  hydrogen  gives  34462  of  these 
units,  or  34462  calories. 

Hydrogen  gas  is  very  seldom  found  in  nature ;  it  occurs 
sometimes  among  the  vapors  which  are  thrown  out  of  vol- 
canoes. But  the  compounds  of  hydrogen  are  everywhere. 
Water  is  only  one  of  them.  Nearly  all  animal  and  vege- 
table bodies  also  contain  hydrogen  in  large  quantities. 

1  One  liter  of  hydrogen  weighs  .0805  g.  when  its  temperature  is 
0^  C.,  and  the  pressure  of  the  air  15  Ibs.  per  sq.  inch. 


CHEMICAL    CHANGES.  33 

QUERY.  —  A  bottle  stands  mouth  downward  in  water;  it  is  full 
of  gas ;  how  would  you  decide  whether  it  contains  air  or  oxygen 
or  hydrogen? 

OXYGEN. 

Oxygen  may  be  obtained  by  heating  mercuric  oxide,  as 
in  Ex.  5,  or  potassium  chlorate,  as  in  Ex.  6.  The  latter 
way  is  better,  and  a  mixture  of  potassium  chlorate  with 
"  black  oxide  "  of  manganese  is  still  better  than  the  chlorate 
alone. 

To  make  Oxygen.  Ex.  S3.  —  I  take  4  g.  of  the  chlo- 
rate and  grind  it  to  powder  in  the  mortar.  To  this  I  add 
2  g.  black  oxide  of  manganese  and  mix  the  two  powders. 
I  put  this  mixture  into  the  side-neck  tube,  Fig.  4,  which  I 
then  cork  tightly  and  fix  in  the  clamp,  as  shown  in  the  cut, 
Fig.  19. 

To  catch  and  hold  the  gas,  I  use  a  set  of  flasks  fitted  up 
as  shown  in  Figs.  18  and  19.  A  conical  flask 
is  provided  with  a  soft  rubber  stopper  with 
two  holes.  A  long  glass  tube  passes  through 
one  of  these  holes  in  the  stopper,  and  almost 
to  the  bottom  of  the  flask ;  a  short  glass  tube 
passes  only  through  the  stopper  in  the  other. 
I  use  four  of  these  flasks,  each  holding  about 
200  cc.1  and  a  small  bottle,  e.  Into  the  first  one,  a,  I  put 
sand  enough  to  cover  the  bottom,  and  then  some  water,  and 
1  also  put  water  into  the  bottle  e.  I  then  join  them  to- 
gether, as  shown  in  Fig.  19,  —  the  long  tube  of  a  with  the 
side-neck  of  the  ignition-tube,  i,  and  the  long  tube  of  each 

1  This  is  a  good  size  for  the  student's  table.  Larger  ones  may  be 
used  by  the  teacher  for  the  class-room,  and  a  flask  may  be  used 
instead  of  the  tube  i  for  larger  quantities.  A  set  once  fitted  up  is 
a  sort  of  general  gas-works  for  the  laboratory,  for,  as  we  shall  see,  this 
method  of  collecting  gas  can  be  used  for  many  other  gases  beside 
oxygen. 


34 


r  /  /  KMICA  L    CIIA  NGEfi. 


of  the  others  with  the  short  tube  of  the  one  before  it, 
the  last  rubber  tube  simply  dipping  into  the  water  of  the 
bottle. 

The  gas  will  be  "washed"  by  bubbling  through  the 
water  in  a,  and  then,  too,  one  can  tell  by  the  bubbles  in  a 

and  in  e  whether 
the  gas  is  coming 
off  fast  or  slow, 
and  can  regulate 
the  heat  accord- 
ingly. The  use 
of  the  sand  will 
be  seen  in  Ex.  27. 
All  the  flasks 
must  be  closed  air- 
tight:; rubber  stop- 
pers easily  make 
air-tight  joints. 
I  now  go  on  to  make  the  gas.  I  make  the  flame  of  the 
Bunsen  just  high  enough  to  not  quite  touch  the  ignition- 
tube,  then  lift  the  lamp  and  heat  the  mixture,  gently  at 
first,  beginning  at  the  part  nearest  the  clamps,  and  mov- 
ing the  flame  to  heat  the  tube  uniformly.  The  decomposi- 
tion of  the  chlorate  will  gradually  go  on  until  it  reaches  the 
bottom  of  the  tube.  If  the  gas  comes  off  too  fast  at  any 
time  I  withdraw  the  heat  for  a  moment. 

The  gas  will  bubble  through  the  water  in  «.,  and  grad- 
ually fill  that  flask,  pushing  the  air  in  it  over  into  the  next 
one,  b.  When  a  is  full,  oxygen  will  go  over  to  the  bottom 
of  b,  and  will  gradually  fill  that  flask,  pushing  the  air  over 
into  c.  From  c  the  air  is  driven  over  to  d,  and  from  d  into 
e,  the  oxygen  filling  them  all.  One  can  be  sure  that  the 
vessels  are  all  filled  with  this  gas  by  putting  a  lighted 
match  into  the  mouth  of  e  ;  the  flame  will  be  brightened. 


Fig.  19. 


CHEMICAL    CHANGES.  35 

When  this  test  shows  that  the  flasks  are  full  of  oxygen,1 
or  when  all  the  chlorate  is  decomposed,  if  in  any  case  too 
little  is  used,  I  withdraw  the  flame,  and  take  off  the  rubber 
tubes  from  all  the  flasks. 

The  Chemical  Change Potassium  chlorate  is  made 

of  potassium,  chlorine,  and  oxygen.  It  gives  up  its  oxygen 
when  heated,  while  the  other  two  elements  are  left  in  the 
tube  combined  with  each  other.  The  manganese  oxide  is 
unchanged,  and  yet  its  presence  is  very  useful,  because  it 
compels  the  chlorate  to  give  up  all  its  oxygen  more  stead- 
ily and  with  less  heat.  But  just  how  it  does  this  is  not 
known.  This  is  one  of  the  cases  in  which  a  substance 
seems  to  act  by  its  presence  simply.  A  chemical  action 
like  this,  that  is,  one  due  to  the  presence  of  a  substance 
which  remains  unchanged,  is  called  catalysis. 

To  discover  the  Properties  of  Oxygen The  flasks, 

used  in  Ex.  23  are  full  of  oxygen. 

What  is  the  color  of  this  gas  ? 

The  bottle  e  is  also  full :  what  is  the  odor  of  oxygen  ? 

The  bottle  has  now  been  standing  some  time  open :  is  it 
still  full  of  gas  ?  If  so,  then  which  is  heavier,  oxygen  or 
air? 

Ex.  24-  —  I  remove  the  stopper  from  flask  d,  hold  the 
flask  bottom  up  for  two  minutes,  then  stand  it  on  the  table 
and  insert  a  lighted  splinter  of  wood. 

Does  the  gas  remain  in  the  flask? 

Then  which  is  heavier,  oxygen  or  air? 

Was  this  also  shown  by  the  bottle  e? 

OXYGEN  AND  THE  MATCH.  Ex.  25.  —  I  wind  a  small 
copper  wire  (No.  20)  around  the  white  end  of  a  burned 
match.  I  then  heat  the  black  end  to  a  glow,  and  lower  it 
a  little  way  into  the  bottle  e.  The  glow  promptly  becomes 

1  The  amount  of  chlorate  used  (4  g.)  will  yield  more  than  enough 
to  fill  these  four  flasks. 


CHEMICAL    CHANGES. 


a  flame.  I  blow  the  flame  out,  and  again  lower  the  spark 
into  the  oxygen ;  the  wood  is  promptly  relighted.  This  may 
be  repeated  many  times  with  the  same  flask  full  of  gas. 

OXYGEN  AND  CARBON.     Ex.  26.  —  I  take  a  piece  of  char- 
coal —  of  the  bark,  if  I  can  get  it  —  and  twist  the  end  of  a 
piece  of  fine  copper  wire  around  it  for  a  handle.     I  then 
heat  one  corner  of  the  charcoal  until  it  glows  and  quickly 
lower  it  into  flask  c.     After  the  burning  is  over  I  pour  a 
little  lime-water  into  the  flask  and  shake  it  well. 
What  effect  has  oxygen  on  the  burning  of  charcoal  ? 
What  effect  is  produced  on  lime-water  afterwards  ? 
What  substance  must  be  present, to  do  this  ?    (See  p.  17.) 
OXYGEN  AND  IRON.     Ex.  27.  —  I  take  a  piece  of  small 
iron  wire  (No.  23),  and  bind  a  piece  of  match  to  one  end 
of  it.     I  then  set  fire  to  the  match  and  place   it  in  the 
mouth  of  flask  a,  lowering  it  slowly 
as  it   burns   away.      The    burning 
wood   heats  the  iron  until    it   too 
takes  fire,  and  it  then  burns  with 
surprising   brightness.      A   slender 
watch  spring  would  burn  with  still 
greater  beauty.     The  sand  catches 
the  melted  globules  of  iron  as  they 
fall,  and  may  save  the  glass  from 
being  broken. 

OXYGEN  AND  HYDRO- 
GEN. Ex.  28.  —  Finally 
in  the  flask  b  I  will  burn 
a  jet  of  hydrogen.  1 
make  the  dry  hydrogen 
as  in  Ex.  22.  The  only 
change  in  the  apparatus 
is  the  addition  of  the  tube  r  t,  Fig.  20 ;  r  is  rubber  and  t  is 
glass,  the  lower  end  of  which  I  held  in  the  flame  until  the 


CHEMICAL    CHANGES.  37 

hole  was  nearly  closed.  Out  of  this  small  hole  the  gas 
comes  in  a  small  jet.  After  the  air  has  been  all  driven  out 
I  set  fire  to  the  hydrogen  and  then  plunge  the  small  flame 
down  into  the  oxygen  in  the  flask,  as  shown  in  the  cut. 

What  change  in  the  appearance  of  the  flame  ? 

What  is  the  new  substance  on  the  walls  of  the  flask  ? 

What  are  the  two  constituents  of  this  substance  ? 

What  must  have  combined  with  the  hydrogen  in  Ex.  22  ? 

Where  did  the  hydrogen  there  get  it  ? 

Description  of  Oxygen. — We  have  found  that  oxygen 
has  neither  color  nor  odor  nor  taste.  It  is  about  1.1  times 
heavier  than  the  same  bulk  of  air.  Oxygen  combines  read- 
ily with  many  things.  It  does  so  very  rapidly  when  heated, 
and  the  chemical  action  yields  both  heat  and  light  as  well 
as  new  substances.  A  chemical  action  which  yields  both 
heat  and  light  is  called  combustion.  The  heat  and  light  of 
all  common  fires  are  due  to  the  action  of  oxygen,  which 
abounds  in  the  air. 

Bodies  which  burn  at  all  in  air  will  burn  with  much 
more  vigor  in  oxygen  alone,  as  did  the  match  and  the  char- 
coal in  Exs.  25,  26.  And  many  things  which  do  not  burn  in 
air  will  burn  freely  in  this  gas,  as  did  the  iron  in  Ex.  27. 

When  a  thing  is  combined  with  oxygen  it  is  said  to  be 
oxidized,  and  the  new  substance  is  called  an  oxide.  Iron  is 
oxidized  when  it  burns  in  dry  oxygen,  and  the  new  sub- 
stance made  is  the  iron  oxide.  Carbon  burned  in  oxygen 
(Ex.  26)  is  oxidized  and  carbon  dioxide  is  produced,  which 
will  show  its  presence  by  whitening  lime-water. 

But  most  substances  must  be  heated  before  they  will 
oxidize  rapidly :  neither  wood  nor  coal  nor  iron  will  burn 
unless  first  made  much  hotter  than  they  can  ever  become 
by  exposure  to  the  greatest  summer  heat.  And  yet  the 
oxygen  of  the  air  is  all  the  time  acting  upon  many  things. 
Wood  decays  and  iron  rusts ;  these  effects  are  due  to 


Cl  I  EM  1C  A  L    CHA  NGES. 

oxygen.     But  they  are  not  produced  quickly.     Substances 
are  oxidized,  at  ordinary  temperatures,  slowly. 

Oxygen  in  Nature.  —  About  one  fifth  part  of  all  the 
atmosphere  is  oxygen  gas,  and  eight-ninths  the  weight  of 
all  the  water  of  the  earth  consists  of  this  element.  In 
the  bodies  of  animals  and  of  plants  oxygen  is  found  in 
large  proportions,  and  in  the  rocks  immense  quantities  are 
combined. 

QUERY.  —  A  bottle  is  full  of  a  colorless  gas ;  how  would  you 
decide  whether  it  is  air  or  hydrogen  or  oxygen? 

Ozone.  —  Oxygen  is  very  strangely  changed  by  the  action 
of  electricity.  If  electric  sparks  are  sent  through  oxygen, 
the  gas  will  be  found  to  have  a  very  strong  and  peculiar 
smell,  a  little  like  that  of  burning  sulphur.  This  strong- 
smelling  oxygen  will  tarnish  silver,  which  remains  bright 
in  oxygen  that  has  not  been  electrified,  and  it  will  do  much 
other  chemical  work  which  common  oxygen  cannot.  Two 
cubic  centimeters  of  it  weighs  as  much  as  three  cubic  centi- 
meters of  oxygen.  In  weight  and  odor  and  in  chemical 
activity  this  electrified  oxygen  is  as  different  from  common 
oxygen  as  if  it  were  another  substance. 

And  yet  it  can  be  nothing  but  oxygen.  For  the  electric 
sparks  cannot  add  anything  to  the  pure  oxygen  they  pass 
through,  and  so  in  going  through  it  they  cannot  make  a 
compound  of  the  oxygen.  And  if  the  oxygen  was  decom- 
posed by  the  sparks,  there  would  be  at  least  another  con- 
stituent set  free  beside  this  one;  but  there  is  not. 

We  must  confess  that  oxygen  has  two  sets  of  properties ; 
the  gas  may  exist  in  two  distinct  forms.  The  heavy,  active, 
strong-smelling  oxygen  is  called  ozone. 

Just  how  the  electricity  changes  oxygen  to  ozone  is  not 
known.  But  one  thing  is  settled -by  experiment,  and  that 
is  that  the  oxygen  is  condensed ;  three  volumes  of  oxygen 


CHEMICAL    CHANG 


will  make  only  two  volumes  of  ozone.  The  electricity  con- 
denses the  oxygen  in  making  ozone. 

Ozone  is  also  made  when  acid-water  is  decomposed  by 
electricity  (Ex.  15).  It  is  found  in  small  quantities  in  the 
atmosphere,  especially  after  thunder-showers,  on  account 
of  the  electric  discharges,  and  its  presence  tends  to  purify 
the  air ;  ozone  oxidizes  the  impurities  quickly  and  makes 
them  harmless. 

Oxygen  is  not  the  only  element1  which  can  exist  in  two 
forms,  as  we  shall  see.  This  property  of  an  element  is 
called  allotropism.  Ozone  is  said  to  be  an  allotropic  form 
of  oxygen. 

EXERCISES  IN  CHEMICAL  ACTION. 

!•  Study  the  action  of  hydrochloric  acid  on  sodium  car- 
bonate by  experiment.  ProcSed  as  follows  : 

1.  Bring  the  two  substances  together  in  a  test-tube,  and 
describe  the  action  which  takes  place. 

2.  Examine  the  gas  which  is  given  off  to  find  out  what 
it  is. 

Note  its  color  and  its  odor. 

Test  it  with  a  flame ;  is  it  oxygen  or  hydrogen  ? 

Is  it  heavier  or  lighter  than  air  ? 

Collect  a  little  of  the  gas  in  another  test-tube.  To  do 
this,  put  a  little  of  the  carbonate  into  a  side-neck  tube,  and 
put  the  rubber  tube  from  this  down  into  a  test-tube.  Make 
a  very  dilute  acid  by  putting  a  cubic  centimeter  into  the 
graduated  cylinder  and  filling  with  water  up  to  25  cc. ;  this 
dilute  acid  will  not  work  quite  so  inconveniently  fast  as 
the  strong.  Now  pour  three  or  four  cubic  centimeters 
upon  the  carbonate,  and  cork  the  side-neck  tube  quickly. 
When  the  action  is  nearly  ended,  add  the  acid  again.  Next 
pour  a  little  lime-water  into  the  test-tube  with  the  gas  and 
shake  it  well. 

1  Sec  definition  of  element  on  p.  24. 


40  CHEMICAL    CHANGES. 

What  gas  does  it  prove  to  be? 

3.  Examine  the  liquid  which  remains  in  the  side-neck 
tube  to  learn  whether  it   contains   any  solid   in   solution. 
Filter  it  (Fig.  9),  if  it  is  not  already  perfectly  clear.     Then 
evaporate  it  (Fig.  10)  until  it  is  dry. 

Compare  the  solid  found  with  the  carbonate  used. 
You  can  recognize  this  new  substance  by  its  taste. 

4.  Write  out  a  short  statement  of  the  facts  which  you 
have  discovered  about  the  action  of  hydrochloric  acid  on 
sodium  carbonate. 

2.  Study  the  action  of  hydrochloric   acid   on    "Baking 
soda."     Do  this  by  experiments  in  just  the  same  way  as 
in  Exercise  1. 

What  are  the  two  proditcts  of  the  action? 
What,  then,  is  "Baking  soda"? 

3.  Study  the  action  of  dilute  sulphuric  acid   on   iron. 
Do  this  by  bringing  the  acid  in  contact  with  some  very 
small  nails  in  a  test-tube,  closing  the  mouth  of  the  tube, 
but  not  quite  air-tight,  with  the  finger.     Then 

Find  out  whether  the  action  is  hastened  by  heat. 

If  a  gas  is  produced,  test  it,  and  name  it. 

Find  out  by  evaporation  whether  a  solid  is  made  also. 
And  finally  write  out  a  short  statement  of  all  the  facts 
which  you  have  discovered  about  the  action  of  dilute  sul- 
phuric acid  on  iron. 

4.  What  is  the  difference  between  a  physical  change  and 
a  chemical    change?      Between   experiment   and   observa- 
tion ?     Between  analysis  and  synthesis  ?     What  are  ele- 
ments ?      WThat   are   compounds  ?      What   are    mixtures  ? 
AVhat,  besides  new  substances,  may  be  produced  by  chemi- 
cal action  ?     What  is  combustion  ?     When  is  a  substance 
said  to  be  oxidized  '.'     What  is  an  oxide  ? 


THE     CHEMISTRY     OF    COMBUSTION. 

IN  ancient  times  only  four  elements  were  supposed  to 
exist,  and  these  were  fire,  air,  earth,  and  water.  It  is  now 
known  that  neither  one  of  these  is  an  element;  and  as 
tojire,  we  know  that  it  is  not  even  a  substance  at  all.  Fire 
is  the  light  and  heat  produced  by  chemical  action.  The 
chemical  action  which  produces  fire  is  called  combustion. 

Between  what  elements  is  this  chemical  action  taking 
place,  and  what  new  substances  are  made  by  it?  These 
are  the  questions  we  now  set  out  to  answer. 

Combustion  of  a  Candle.  Ex.  29.  —  I  bring  a  clean  and 
dry  bottle  down  over  the  flame  of  a  burning  candle  and 
hold  it  there  for  a  little  while,  as  shown  in  Fig.  21. 

What  is  the  effect  on  the  flame  ? 

What  gathers  on  the  walls  of  the  bottle  ? 

Will   lime-water  be    whitened  if   shaken  in  the  bottle? 

Thus  we  find  water  and  carbon  dioxide  both  made  by  the 
burning  candle.  But  we  know  that  it  takes  hydrogen  and 
oxygen  to  form  water  (Ex.  28),  and  also 
that  the  air  can  furnish  the  oxygen 
(Ex.  22).  So,  when  the  candle  burns,  the 
air  must  furnish  oxygen,  and  the  can- 
dle must  furnish  hydrogen  to  form  the 
water  which  it  produces. 

In  Ex.  26  we  found  that  carbon  diox- 
ide is  made  of  carbon  and  oxygen.     The 
carbon  dioxide  of  the  candle-flame  must 
contain  these  same  elements.      The  oxy- 
gen could  come  from  the  air ;  the  carbon  must  have  come 
from  the  candle.     Clearly  the  candle  must  contain  carbon 
and  hydrogen  among  its  elements.     And  when  it  burns, 


42  CHEMISTRY    OF    COMBUSTION. 

the  chemical  action  is"  between  oxygen  of  the  air  and  these 
elements  of  the  candle. 

Combustion  in  other  Cases.  Ex.  30.  —  Burn  a  splin- 
ter of  wood,  a  small  roll  of  paper,  a  bit  of  cotton  on  a  wire 
and  moistened  with  alcohol,  and  a  small  jet  of  gas  from 
the  Bunsen  lamp,  in  dry  bottles,  and  see  whether  you 
lind  the  same  two  products  in  each  case. 

In  the  burning  of  a  candle,  of  wood,  of  paper,  of  alcohol, 
of  gas,  —  and  in  f act  of  all  other  common  fuels,  —  the  com- 
bustion is  simply  the  combination  of  oxygen  with  the 
constituents  of  these  substances. 

Carbon  and  hydrogen  make  up  by  far  the  larger  part 
of  all  the  substances  which  are  used  for  fuel,  and  when  the 
fuel  burns  carbon  dioxide  and  water  are  always  the  chief 
products.  When  wood  burns  it  is  first  decomposed  by 
heat.  Its  carbon  and  hydrogen  then  take  oxygen  from  the 
air  and  make  carbon  dioxide  and  water-vapor,  and  these 
two  gases  pass  away  in  the  smoke. 

Why  did  the  flames  all  go  out  in  the  bottle? 

The  black  part  of  smoke  is  the  carbon  which  goes  off 
without  burning. 

A  smoky  flame  is  one  that  gets  too  little  air.  A  lamp 
without  a  chimney  smokes,  but  with  a  chimney  the  flame  is 
clear  and  bright.  It  is  so  because  the  hot  chimney  makes 
a  current  of  air  sweep  past  the  flame  all  the  time,  and  this 
large  quantity  of  air  gives  oxygen  enough  to  burn  the 
carbon  completely.  In  every  common  fire  much  fuel  is 
wasted  as  smoke,  because  the  furnace  is  not  built  in  a  way 
to  furnish  air  enough  to  burn  up  all  the  carbon. 

Combustion  is  a  mutual  chemical  action,  generally  be- 
tween oxygen  and  some  other  substance,  and  which,  when 
rapid  enough,  evolves  heat  and  light. 

When  a  substance  will  burn  in  air,  it  is  said  to  be  cam- 


CHEMISTRY    OF    COMBUSTION.  43 

bustible :  the  air  at  the  same  time  is  said  to  be  the  sup- 
porter of  combustion.  But  really  there  is  no  difference 
in  the  part  played  by  the  two  things  in  the  action :  the 
chemical  change  is  mutual. 

Heat  a  Product  of  Combustion Fuel  is  burned  for 

the  sake  of  the  heat  it  can  give,  and  not  for  the  sake  of 
the  new  compounds  which  it  yields.  The  hottest  kind 
of  flame  is  that  of  hydrogen  burning  with  oxygen.  It  is 
called  the  ox //hydro yen  flame. 

Fig.  22  shows  how  this  flame  is  obtained.  The  two  gases 
are  in  separate  bags,  H  and  0,  or  sometimes  in  iron  cylin- 


Fig.  22. 

ders.  They  are  pressed  out  of  these  through  separate  tubes 
into  the  " oxyhydrogen  jet,"  where  they  mix  just  before 
they  reach  the  fire  at  the  end  of  the  jet. 

The  two  gases  unite  to  form  water,  which  goes  away  as 
vapor  into  the  air.  This  chemical  action  is  the  source  of  a 
heat  so  intense  that  wires  or  strips  of  iron,  steel,  copper, 
zinc,  and  other  things  that  do  not  burn  at  all  in  common 
fires,  will  burn  in  it  almost  as  fast  as  a  cotton  thread  will 
burn  in  a  lamp-flame. 

If  we  burn  hydrogen  in  air  instead  of  in  oxygen  the  heat 
is  less  intense  because  the  chemical  action  is  hindered  by 
the  large  quantity  of  nitrogen  which  air  contains. 


44  CHEMISTRY    OF    COMBUSTION. 

The  quantity  of  heat  will  depend  on  the  quantity  of 
hydrogen  which  burns.  Two  grams  of  hydrogen  will  yield 
exactly  twice  as  much  heat  as  one  gram,  no  matter  whether 
it  burns  slowly  or  swiftly.  But  if  it  burn  swiftly,  more 
heat  will  be  given  in  the  same  time,  and  the  heat  will  be 
more  intense. 

If  a  gram  of  hydrogen  burns  in  the  air  instead  of  in 
oxygen  it  will  still  give  the  same  quantity  of  heat,  and 
yet  the  heat  will  not  be  as  intense  even  if  it  burn  in  the 
same  time,  because  some  part  will  be  used  in  heating  up 
the  large  amount  of  nitrogen  in  air. 

We  may  say  the  same  things  of  the  heat  when  carbon 
or  any  other  element  is  burned.  The  quantity  of  heat  will 
always  be  the  same  for  the  same  weight  of  the  element 
burned,  while  the  intensity  of  the  heat  will  depend  on  the 
time  it  takes  to  burn  it. 

But  there  is  this  difference,  the  gram  of  hydrogen  will 
give  more  heat  than  the  gram  of  carbon.  There  is  just 
a  certain  amount  of  heat  which  the  burning  of  a  gram  of 
each  element  will  give,  but  this  quantity  is  not  the  same 
for  any  two  of  them. 

Heat  Required  to  Start  Combustion A  jet  of  gas, 

such  as  that  from  a  chandelier,  for  example,  escaping  into 
the  air,  shows  no  signs  of  "taking  fire,"  but  touch  it  witli 
a  match-flame,  and  it  instantly  springs  into  vivid  combus- 
tion. What  has  the  match-flame  done  ?  It  has  simply 
heated  the  gas.  Illuminating-gas  will  not  burn  until  it  has 
a  temperature  of  about  1000°  F.,  and  when  the  fire  of  the 
match  has  heated  the  jet  up  to  this  temperature  it  bursts 
into  flame. 

The  temperature  at  which  a  substance  begins  to  burn  in 
air  is  called  its  kindling-point.  The  kindling-point  of  most 
of  our  ordinary  fuels  is  about  1000°  F.,  but  some  other 
things  begin  to  burn  at  a  much  lower  temperature.  Phos- 


CHEMISTRY    OF    COMBUSTION.  45 

phorus,  for  example,  kindles  at  a  temperature  little  higher 
than  that  of  our  fingers  when  we  handle  it. 

The  kindling-point  of  a  substance  is  the  temperature  at 
which  it  will  begin  to  burn. 

In  lighting  a  gas-jet  the  match-flame  is  needed  only  to 
heat  the  gas  up  to  its  kindling-point. 

All  Flames  are  Gas  Flames.  —  Let  the  wick  of  an  alco- 
hol-lamp be  uncovered ;  no  signs  of  flame  are  to  be  seen, 
but  touch  it  with  a  lighted  match,  and  very  quickly  an  alco- 
hol flame  appears.  Now,  the  wick,  to  begin  with,  is  wet 
with  liquid  alcohol.  Then  the  heat  of  the  match  changes 
this  liquid  into  vapor,  and  afterward,  quickly  heats  this 
vapor  up  to  its  kindling-point.  When  this  double  work  is 
done  the  flame  appears. 

The  alcohol  is  in  a  gaseous  form  when  it  burns  with  a 
flame. 

We  will  suppose,  next,  that  we  have  a  candle  which  has 
been  lighted  and  partly  burned  on  some  previous  occasion. 
Its  wick  is  saturated  with  cold  and  solid  wax.  We  touch  it 
with  a  match-flame.  We  notice  that  it  takes  more  time  to 
fire  it  than  it  does  a  spirit-lamp  or  a  gas-jet.  The  match 
has  more  work  to  do.  It  first  melts  the  wax ;  it  next 
changes  it  into  vapor ;  and  then,  finally,  it  heats  the  vapor 
up  to  its  Idndliny-point.  Not  until  this  threefold  work  is 
done  does  the  candle-flame  appear.  The  wax  is  in  the  form 
of  gas  when  it  burns  with  flame. 

The  wax  of  the  candle,  and  the  alcohol  of  the  lamp,  are 
changed  into  gases  before  any  flame  is  seen,  and  this  is 
true  of  other  fuels  also.  Whatever  burns  with  a  flame  must 
be  at  that  moment  in  a  (/aseous  state. 

Wood  burns  with  flame,  because  it  is  first  decomposed 
by  the  heat.  Gases  are  formed,  and  the  burning  of  these 
gases,  and  not  of  the  solid  wood,  produces  the  flame. 

Hard-coal    is  made    up  almost   entirely  of  solid   carbon. 


46  CHEMISTRY    OF    COMBUSTION. 

which  no  furnace-heat  can  change  into  gas.  As  there  are 
no  gases  first  made  by  the  heat,  so  there  can  be  no  flame 
produced  in  the  burning.  Hard-coal  burns  with  a  steady 
glow  without  flame. 

This  is  true  if  there  is  plenty  of  air  for  all  the  carbon, 
but  sometimes  there  is  not,  and  then  carbon  dioxide  is 
formed,  at  first,  as  usual.  But  this  afterward  shares  its 
oxygen  with  more  carbon  and  becomes  carbon  monoxide. 
This  carbon  monoxide  is  a  gas,  and  burns  with  a  blue  flame, 
which  may  be  often  seen  playing  over  the  surface  of  a  hard- 
coal  fire. 

Light  a  Product  of  Combustion The  very  hot  flame 

of  hydrogen  gives  very  little  light,  but  if  I  hold  a  small 
iron  wire  in  this  flame  the  wire  will  quickly  glow  with 
light  of  a  bright-red  color.  If  a  piece  of  lime  is  held  in  the 
oxyhydrogen  flame  it  will  shine  with  a  dazzling  brightness. 
The  light  made  in  this  way  is  the  well-known  "  lime  light," 
also  called  the  oxyhydrogen  light. 

In  both  these  cases  the  light  is  made  by  heating  a  solid 
substance  which  will  not  melt  nor  become  a  gas.  Any 
flame  which  contains  a  solid  substance  which  will  not 
melt,  nor  become  a  vapor  when  heated,  is  a  light-giving 
flame.  Is  there  such  a  solid  substance  in  a  candle  or  a 
gas  flame? 

Ex.  31.  —  I  take  a  square  of  clean  dry  window-glass  and 
hold  it  for  a  very  short  time  across  a  candle-flame,  just  be- 
low the  tip  of  it.  I  must  remove  it  before  it  gets  hot. 

What  products  are  deposited  on  the  glass? 

Ex.  32.  —  I  close  the  holes  in  the  tube  of  the  Bunsen 
burner  and  the  flame  at  once  becomes  bright.  I  next 
press  a  clean  dry  cold  glass  down  upon  it  as  I  did  upon 
the  candle-flame  before,  and  notice 

Whether  the  same  products  are  left  on  it. 


CHEMISTRY    OF    COMBUSTION.  47 

7£r.  33.  —  Open  the  holes  of  the  Bunsen  burner  and  let 
the  air  enter.  It  mixes  with  the  gas  in  the  tube,  and  there 
is  then  oxygen  enough  among  the  particles  of  gas  to  satisfy 
both  the  hydrogen  and  the  carbon  at  once. 

Compare  the  light  with  that  when  the  holes  are  shut. 

The  candle-flame  and  the  gas-flame  both  leave  a  black 
coat  upon  the  cold  surface  of  the  glass,  and  outside  this 
spot  a  ring  of  dew  may  be  seen.  The  black  substance  is 
carbon.  The  wax  of  the  candle  contains  hydrogen  and 
carbon.  Now,  when  these  two  are  offered  to  oxygen  the 
oxygen  will  take  hydrogen  first.  This  is  one  fact.  An- 
other is,  that  carbon  is  a  solid  which  will  not  melt. 

We  can  now  see  how  the  light  of  a  common  flame  is 
made.  The  burning  substance  is  decomposed  into  hydro- 
gen and  carbon.  The  oxygen  of  the  air  combines  with  the 
hydrogen  first,  and  produces  water,  and  great  heat.  This 
heats  the  particles  of  the  carbon  white-hot,  so  that  they 
shine  with  a  bright  light. 

But  the  next  moment  this  white-hot  carbon  unites  with 
oxygen  of  the  air,  and  is  changed  at  once  into  invisible 
carbon  dioxide. 

If  the  hydrogen  and  oxygen  both  burn  at  the  same  in- 
stant little  light  is  given  by  the  flame.  The  carbon  changes 
to  carbon  dioxide  as  fast  as  the  hydrogen  does ;  its  par- 
ticles do  not  remain  free  long  enough  to  shine.  This  is 
also  the  reason  that  the  Bunsen  flame  is  smokeless.  The 
oxygen  of  air  is  mixed  all  through  the  gas  and  burns  the 
carbon  as  fast  as  it  is  set  free. 

But  the  heating  of  solid  particles  in  a  flame  is  not  the 
only  cause  of  the  light.  It  has  been  found  that  some  of 
the  light  comes  from  dense  gases  in  the  flame  as  well  as 
from  the  solid  particles.  This  explains  why  a  lamp-flame 
is  not  so  bright  on  the  top  of  a  high  mountain  as  it  is  at  the 
base.  The  gases  in  the  flames  are  denser  at  the  base,  where 


48 


CHEMISTRY    OF    COMBUSTION. 


the  atmosphere  is  heavier,  than  they  are  at  the  top  of  the 
mountain. 

A  Common  Flame  is  Hollow.  Ex.  34.  —  I  lay  the 
stick  of  a  common  match  right  across  a  good  candle-flame, 
just  above  the  top  of  the  wick,  and  leave  it  there  only  long 
enough  for  the  flame  to  scorch  it.  Where  it  is  not  scorched 
of  course  there  is  no  fire. 

Where  is  the  fire,  as  shown  by  the  stick? 

Ex.  35.  —  I  take  a  square  of  paper  and  press  it  down 
upon  the  candle-flame  almost  to  the  top  of  the  wick  and 
take  it  away  again  just  as  soon  as  I  begin  to  see  the  upper 
surface  blacken,  as  shown  in  Fig.  23. 

Where  is  the  fire,  as  shown  by  the  charred  paper  ? 


Ex.  36.  —  The  larger  flame  of  an  alcohol-lamp  is  better 
for  the  last  two  experiments  than  the  candle.     I  plunge 

the  head  of  a  match  in- 
to the  dark  center  above 
the  wick.  The  wood  of 
the  match  burns  in  the 
edge  of  the  flame,  but 
the*  head  of  the  match 
in  the  center  does  not. 

What  is  lacking,  heat 
or  air,  or  both  ? 

In  a  candle  or  lamp 
flame  the  combustion  goes  on  only  around  the  outside,  — 
in  other  words,  the  flame  is  hollow.  There  is  no  oxygen 
in  the  center  of  the  candle  or  the  gas  flame.  The  dark 
space  there  is  filled  with  the  hot  vapor  of  the  wax  or 
with  gas,  and  the  combustion  goes  on  only  where  the  air 
is  in  contact  with  the  outside  of  this  vapor. 

The  burner  of  a  chandelier  is  made  so  as  to  spread  the 
illuminating-gas  out  into  a  fan-shaped  sheet.     This  brings 


Fig.  23. 


CHEMISTRY    OF    COMBUSTION.  49 

a  larger  surface  to  the  air  and  makes  more  light,  but  the 
chemical  action  is  only  on  the  outside  of  this  thin  sheet. 
The  argand  oil-burner  does  the  same  thing  in  another  way. 
Its  wick  is  thin  and  cylindrical,  and  air  is  made  to  pass  up 
through  the  inside  of  it.  The  inside  and  outside  together 
form  a  large  surface.  And  then  by  using  a  chimney  a 
draught  is  made  by  which  more  air  than  otherwise  must 
pass  up  over  the  surface  of  the  flame.  The  best  light  is 
produced  by  securing  a  full  supply  of  air  and  a  large 
surface  to  the  flame. 

QUERIES.  —  What  will  be  the  effect  of  cooling  a  flame  to  a  tem- 
perature below  the  kindling-point? 

If  a  large  piece  of  flat  iron  or  stone  is  laid  across  a  flame,  as  the 
paper  was  laid  in  Ex.  35,  the  flame  will  not  touch  it ;  a  thin  space 
between  them  can  be  seen  (try  it).  Why  does  the  flame  not  touch 
the  solid? 

Does  a  flame  actually  touch  the  bottom  of  a  kettle  in  whicli 
water  is  being  heated?  Why? 

Why  will  a  flame  not  pass  through  wire  gauze  ?  But  what  if 
the  gauze  becomes  red-hot  ? 

Why  does  blowing  a  candle  quench  the  flame  ?  Why  does  blow- 
ing a  fire  make  it  burn  more  briskly  ? 


THE    CHEMISTRY    OF    WATER. 

Analysis  and  Synthesis.  —  We  have  seen  that  there 
are  two  ways  of  finding  the  composition  of  a  compound : 
one  is  called  analysis,  the  other  synthesis.  In  analysis  we 
decompose  the  compound  in  such  a  way  as  to  show  what  it 
is  composed  of,  while  in  synthesis  we  combine  the  con- 
stituents in  such  a  way  as  to  show  what  they  make. 

Experiment   28   was  a  synthesis  of   water,  because   we 


Fig.  24. 

brought  hydrogen  and  oxygen  together  and  found  that 
they  produced  water  when  they  combined.  That  experi- 
ment proved  that  water  is  composed  of  hydrogen  and  oxy- 
gen. But  this  is  not  enough.  We  wish  to  know  whether 
it  makes  any  difference  if  we  use  more  or  less  of  these  ele- 
ments, and  if  it  does,  then  we  wish  to  know  just  how  much 
of  each  is  needed.  Now  that  we  know,  by  synthesis,  what 
the  elements  of  water  are,  \ve  will  try,  by  analysis,  to  find 
DO 


CHEMISTRY    OF    WATER.  51 

out  whether  there  is  any  particular  quantity  of  each,  and  if 
so,  then  how  much  the  water  contains. 

Analysis  of  Water.  Ex.  87.  —  How  can  we  decompose 
water  ?  We  have  already  found  in  Ex.  15  that  electricity 
will  set  hydrogen  free  from  acidulated  water,  and  we  will 
try  electricity  for  our  purpose  now. 

APPARATUS  NEEDED.  —  We  must  have  a  battery,  B,  to 
furnish  the  electricity;  two  wires,  w  w,  to  carry  the  elec- 
tricity into  the  water ;  two  graduated  cylinders,  to  catch 
the  gases,  the  water-pan  and  the  support.  All  these  are 
shown  in  Fig.  24. 

THE  BATTERY. — Two  cells  of  any  good  battery  will  de- 
compose water  slowly,  and  a  larger  number  more  rapidly. 
If  a  battery  is  not  at  hand,  one  can  be  easily  made  as 
follows : l 

TO    MAKE    THE    TEST-TUBE    BATTERY.  Take  20  inches  of 

round  "  carbon  pencil, "  used  in  small  electric  lamps.  It 
should  be  about  ^-inch  diameter,  and  cost  a  few  cents. 
Saw  this  into  five  lengths  of  four  inches  each. 

Find  five  nails,  each  about  the  same  length  as  the  car- 
bons, and  place  them  in  a  dish  of  dilute  sulphuric  acid. 
The  acid  will  dissolve  off  the  smooth,  hard  surface  of  new 
nails,  so  that  they  will  act  quickly  when  put  into  the  bat- 
tery-fluid by  and  by. 

Get  some  flexible  copper  wire,  —  No.  18  is  a  good  size  to 
wind  easily, — and  finally  also  get  the  rack  of  test-tubes 
and  a  pair  of  pincers. 

Take  a  piece  of  the  wire  about  four  inches  long,  and 
wind  one  end  of  it  around  the  end  of  a  carbon  rod  twice, 
as  tightly  as  it  can  be  drawn,  and  then,  lapping  the  short 
end  over  the  wire,  twist  them  with  the  pincers.  This 
makes  a  close,  firm  joint.  See  Fig.  25,  c.  Then  take  one 

1  My  test-tube  battery  is  cheaply  and  easily  made,  and  works  vigor- 
ously. It  is  fairly  constant  for  an  hour  and  a  half.  It  will  yield 
hydrogen  from  acid-water  at  the  rate  of  1  cc.  per  minute. 


52  ciiKuisTiiY  OF   \\'ATh:n. 


of  the  nails,  ?i,  and  wind  the  other  end  of  the  wire  around 
it  just  below  the  head,  drawing  the  wire  as  tightly  as  pos- 
sible. Roll  the  wire  upon  the  nail  until  the  carbon  and 
nail  are  just  far  enough  apart  to  let  the  couple  hang  close 
against  the  inside  of  two  tubes  when  they  stand  in  the  rack, 
as  shown  at  B,  in  Fig.  25  and  Fig.  24.  Make  four  of  these 
couples  and  hang  them  in  the  tubes,  so  that  there  will  be 
a  carbon  and  a  nail  in  each,  except  the  first  and  the  last. 
The  carbons  and  nails  must  not  touch  one  another.  Then 
fix  one  carbon  without  a  nail,  and  one  nail  without  a  car- 
bon, C,  Fig.  25.  Put  the  carbon  in  the  tube  with  the  lone 
nail,  and  the  nail  in  that  with  the  lone  carbon,  and  put  the 
ends  of  their  wires  into  the  small  holes  ht  Fig.  24,  made 
with  an  awl  in  the  top  of  the  rack. 

THE  WIRES.  —  Cut  two  strips  of  platinum  foil,  each  an 
inch  long  and  a  little  less  than  half  an  inch  wide,  and  two 
covered  copper  wires,  say  twenty. 
inches  long.  Make  one  end  of  each 
wire  very  bright  ;  crowd  it  through 
a  small  hole  near  the  end  of  a  plati- 
num strip,  bend  it  back  on  the  other 
si^le,  and  press  the  loop  carefully  but 
tightly  together  to  hold  the  platinum 
firmly.  Now  lay  a  thin  piece  of  solder  on  the  wire  where 
it  touches  the  platinum,  moisten  it  with  a  drop  of  hydro- 
chloric acid,  and  then  hold  it  in  the  blue  flame  of  the  Bun- 
sen  lamp  until  the  solder  melts,  and  no  longer,  lest  the 
solder  corrode  and  ruin  the  foil.  In  this  way  the  wire  and 
foil  will  be  "  soldered  "  together. 

The  ^junctions  of  the  platinum  and  wires,  and  so  much  of 
the  wires  themselves  as  will  be  in  the  water,  must  be  well 
covered  with  paraffine.  Melt  some  paraffine  over  a  gentle 
heat,  and  before  the  liquid  has  'become  very  hot  put  the 
lower  end  of  the  platinum  and  wire  into  it. 
See  the  foot-note  on  page  54. 


CHEMISTRY    OF    WATER.  53 

THE  GRADUATED  CYLINDERS.  —  Use  two  of  the  gradu- 
ated cylinders  shown  at  a,  in  Fig.  1.  To  support  them : 
saw  two  slots  in  a  piece  of  thin  board 
(Fig.  26,  ft),  and  then  fasten  it  in  the 
clamp  of  the  support  /,  Fig.  5.  The 
cylinders  will  hang  bottom  upward 
through  these  slots,  as  shown  in 
Fig.  24. 

THE  WATER.  —  Pure  water  will 
not  let  electricity  go  through  it,  but 
if  it  contains  some  sulphuric  acid  the  electricity  will  go 
freely.  Use  about  one-thirtieth  as  much  strong  acid  as 
water,  and  fill  the  water-pan  deep  enough  to  cover  the 
tops  of  the  platinum  strips  half  an  inch  when  they  stand 
upright,  as  shown  in  Fig.  26,  a. 

THE  BATTERY  FLUID.  —  Dissolve  35  g.  of  powdered  po- 
tassium dichromate  in  200  cc.  of  hot  water.  Then  add 
24  cc.  of  strong  sulphuric  acid  very  slowly?  all  the  time 
stirring  the  liquid.  Use  it  when  cold. 

THE  EXPERIMENT.  —  Fill  the  cylinders  by  laying  them 
in  the  pan  of  water,  and  then,  lifting  them  bottom  up,  care- 
fully rest  them  in  their  support,  as  shown  in  Fig.  24. 

Not  a  bubble  of  air  should  remain  in  either  one. 

Bend  the  wires  to  bring  the  platinum  strips  up  under  the 
mouths  of  the  cylinders,  and  fix  them  in  place  by  bending 
them  tightly  over  the  edge  of  the  pan.  See  Fig.  26,  a,  and 
Fig.  24.2 

1  Great  heat  is  produced  by  adding  the  strong  acid,  and  there  is 
danger  that  drops  of  the  hot  liquid  will  fly  out  of  the  vessel.    Let  the 
acid  run  down    the  side  of  the  vessel  in  a  very  small  stream  while 
the  red  liquid  is  kept  in  motion. 

2  Or,  better,  the  wires  may  be  passed  up  behind  the  cylinders 
through  small  holes  in  the  wooden  support.    The  wires  may  be  wedged 
tightly  in  these  holes,  and  the  platinum   strips   will  then  be  held  in 
place  firmly  while  the  wires  are  being  handled  during  the  experiment. 


54  CHEMISTRY    OF    WATER. 

Next,  fill  the  test-tubes  nearly  full  of  the  battery  fluid, 
put  globules  of  mercury  into  the  holes  h,  and  finally  put 
the  ends  of  the  wires  from  the  water-pan  into  these  holes, 
noting  by  the  watch  the  time  when  the  last  is  inserted. 

Bubbles  of  gas  instantly  form  on  the  platinums,  break 
away,  and  rise  into  the  cylinders;  see  that  none  escape 
outside. 

Note  the  number  of  cubic  centimeters  of  gas  in  each 
cylinder : 

At  the  end  of  2  minutes. 

At  the  end  of  5  minutes. 

At  the  end  of  10  minutes. 

Do  you  find  the  larger  quantity  over  the  platinum  which 
is  joined  to  the  carbon  or  to  the  iron  of  the  battery  ? 

Which  is  Hydrogen  and  which  is  Oxygen  ?  Ex.  38. — 
I  test  the  gases  with  a  match-flame.  Holding  a  lighted 
match  in  my  right  hand,  I  grasp  the  cylinder  which  is 
over  the  plantinum  of  the  wire  which  comes  from  the  iron 
of  the  battery,  and,  closing  its  mouth  as  well  as  I  can 
with  my  thumb,  I  lift  it  out  of  the  water,  turn  it  quickly 
mouth  upward,  and  at  the  same  time  bring  the  flame  to 
its  mouth.  The  gas  burns  with  explosion. 

I  next  test  the  gas  in  the  other  cylinder  in  the  same  way ; 
the  match  burns  with  unusual  brilliancy,  or  a  long  splinter 
of  wood  with  a  spark  of  fire  thrust  down  into  the  gas 
bursts  into  flame. 

What  are  the  relative  volumes  of  hydrogen  and  oxygen  ? 

The  Facts The  current  of  electricity  decomposes  the 

acid  water.  Hydrogen  and  oxygen  are  the  only  substances 
produced.  And  there  are  always  twice  as  many  cubic  cen- 
timeters of  hydrogen  as  of  oxygen.1 

1  Oxygen  combines  with  copper,  and  if  the  wires  and  solder  are  not 
completely  covered  with  paraffine  where  they  touch  the  liquid,  some  of 
the  oxygen  will  be  used  up  in  this  way. 


CHEMISTRY    OF    WATER.  55 

These  facts  mean  that  water  is  made  up  of  two  measures 
of  hydrogen  and  one  measure  of  oxygen. 

A  Source  of  Doubt But  the  water  was  not  pure,  and 

some  part  of  these  gases  may  have  come  from  the  acid  in  it, 
or  have  been  used  up  by  it.  So  this  analysis  alone  does  not 
prove  the  composition  of  water  beyond  doubt.  In  fact,  it  is 
only  one  source  of  evidence,  while  there  are  many  others.1 
We  may  mention  one.  By  measuring  the  hydrogen  and 
oxygen  gases,  and  then  passing  an  electric  spark  through 
the  mixture,  they  are  made  to  combine,  and  in  every  case 
it  is  found  that  just  twice  as  many  cubic  centimeters  of 
hydrogen  as  of  oxygen  have  been  used  to  produce  water. 

All  the  facts  when  taken  together  prove  that  pure  water 
is  composed  of 

Two  volumes  of  hydrogen  and  one  volume  of  oxygen. 

Composition  by  Weight.  —  But  hydrogen  is  much 
lighter  than  oxygen.  In  fact,  it  is  found  that  one  measure 
of  oxygen  weighs  eight  times  as  much  as  the  two  measures 
of  hydrogen.  So  that  by  weight,  pure  water  is  composed  of 

One  part  of  hydrogen  and  eight  parts  of  oxygen. 

One  ninth  part  of  any  weight  of  water  is  hydrogen,  and 
the  other  eight  ninths  of  it  is  oxygen. 

Then  how  much  of  each  must  there  be  in  100  grams  ? 
One  ninth  of  a  hundred,  or  11.11  of  hydrogen,  and  eight 
ninths  of  a  hundred  or  88.89  of  oxygen.  The  chemist 
writes  this  composition  of  water  thus: 

Hydrogen 11.11 

Oxygen 88.89 

Water 100.00 

And  this  is  called  the  percentage  composition  of  water. 
Composition  by  Volume.  —  We   have   just   seen  that 
water  when  it  is  decomposed  yields  just  twice  as  many 
1  See  Roscoe  and  Schoiiemmer,  pp.  204,  212. 


56  CHEMISTRY    OF    WATER. 

cubic  centimeters  of  hydrogen  as  of  oxygen.  When  we 
had  20  cc.  of  hydrogen  we  had  also  just  10  cc.  of  oxygen. 
But  we  did  not  notice  how  much  water  gave  us  the  20  cc. 
of  one  and  the  10  cc.  of  the  other.  The  fact  is  that  it 
takes  only  about  fa  part  of  1  cc.  of  the  liquid,  and  this  is 
so  small  a  quantity  that  we  do  not  see  the  loss  of  it  in 
the  experiment. 

But  while  20  cc.  of  hydrogen  and  10  cc.  of  oxygen  will 
make  so  little  of  the  liquid  water,  they  will  of  course  make 
a  great  deal  larger  volume  of  water  vapor.  It  has  been 
found  that  they  will  make  just  20  cc.  The  volume  of  the 
water,  in  vapor,  is  just  the  same  as  the  volume  of  the 
hydrogen  alone.  The  fact  is  that 

Two  measures  of  hydrogen  and  one  measure  of  oxygen 
make  two  measures  of  water-vapor.  Or  three  volumes  of 
the  constituents  are  condensed  to  two  volumes  of  the  com- 
pound. 

Make  a  note  of  this  curious  fact. 

The  Constant  Composition  of  Water Water  has 

been  analyzed  over  and  over  again  with  the  same  result. 
The  synthesis  of  water  also  has  been  repeated  a  great  many 
times,  and  the  same  proportions  of  the  same  elements  have 
always  been  found.  It  is,  therefore,  quite  certain  that  pure 
water  is  always  made  up  of  the  same  elements  and  in  the 
same  proportions  by  volume  and  by  weight. 

The  Constant  Composition  of  other  Compounds. — 
We  may  mention  hydrochloric  acid.  It  has  been  proved 
by  both  analysis  and  synthesis  that  this  acid  is  always 
made  up  of  hydrogen  and  chlorine,  in  the  proportions  of 
1  part  by  weight  of  hydrogen  to  35.5  parts  of  chlorine. 
Its  composition  is  as  constant  as  that  of  water. 

And  common  salt,  from  whatever  source  it  comes,  always 
contains  the  same  two  elements,  —  chlorine  and  sodium . 
and  always  in  the  proportions  of  .'>.">. 5  parts  of  chlorine  to 
23  of  sodium. 


CHEMISTRY    OF    WATER.  57 

The  Law  of  Constant  Proportions.  —  So  many  com- 
pounds have,  like  these  just  named,  been  found  to  have  a 
constant  composition,  that  the  chemist  is  quite  sure  that 
all  compounds  are  alike  in  this  respect,  and  he  states  this 
conclusion  as  follows : 

Any  compound  is  ahvays  made  of  the  same  constituents 
and  in  the  same  invariable  proportions. 

This  important  statement  of  fact  is  known  as  the  law  of 
constant  proportions. 

Water  in  Nature.  —  Hydrogen  and  oxygen  are  the  only 
constituents  of  all  pure  water.  Bat  pure  water 
is  not  to  be  found  in  nature.  Even  the  rain- 
drop, which  has  never  touched  anything  but  the 
air  through  which  it  falls,  is  not  pure,  and  it  is 
still  more  impure  after  it  has  touched  the  earth. 
Why  is  water  always  impure  ?  And  what  are 
its  impurities  ?  These  are  the  questions  which 
we  will  try  next  to  answer. 

]$Xt  QQ^  —  I  fill  a  bottle  three-fourths  full  of  clear  water. 
I  cover  it  with  a  piece  of  muslin  loosely,  and  bind  the  cover 
in  place  by  a  string  around  the  neck.  I  put  half  a  tea- 
spoonful  of  powdered  cochineal  011  the  cover,  and  then  pour 
some  clear  water  slowly  upon  it.  The  water  very  soon 
trickles  through  the  cover  and  falls  into  the  water  below. 
But  instead  of  being  clear  and  colorless,  it  falls  from  the 
cover  in  a  crimson  stream.  Why  ? 

Ex.  40.  —  I  repeat  Ex.  39,  but  in  place  of  the  cochineal 
I  use  some  powdered  copper  sulphate.  The  stream  which 
falls  into  the  water  is  Hue.  Why  ? 

Ex.  41.  —  I  prepare  a  flask  of  hydrochloric  acid  gas  in 
this  way :  I  put  40  or  50  cc.  of  strong  hydrochloric  acid  into 
a  side-neck  flask,  /,  Fig.  28,  and  fix  the  flask  in  the  clamp  of 
the  support.  1  join  the  side-neck  to  the  long  tube  of  the 


58  CHEMISTRY    OF    WATER. 

flask  a,  and  the  short  tube  of  a  with  the  long  tube  of  b. 
And  now,  all  the  joints  being  tight,  I  gently  heat  the  acid. 

Hydrochloric  acid  gas  will 
go  over,  driving  the  air  be- 
fore it,  until  the  flasks  are 
full.  When  the  gas  issues 
freely  from  b  it  will  make 
itself  known  ;  then  I  with- 
draw the  flame,  and  at  once 
take  both  rubber  tubes  from 
a.  I  then  take  the  stopper 
from  the  flask,  and  at  the 
same  time  cover  its  mouth 
28-  with  the  palm  of  my  hand. 

I  now  turn  the  flask  bottom  upward  and  lower  its  mouth 
into  t^e  water  of  the  pan,  as  shown  in  Fig.  29.  The  water 
rises  —  it  should  rise  quickly  —  into  the  flask.  Why  ? 

Cochineal  readily  mixes  with  water,  and  gives  it  a  crim- 
son color.  And  yet  not  a  particle  of 
cochineal  can  be  seen  in  the  crimson 
liquid.  It  is  divided  into  pieces  too 
small  to  be  seen,  and  these  pieces  are 
uniformly  scattered,  giving  color  to 
every  part.  The  cochineal  was  dis-  "»•  29 

solved  by  the  water.  The  red  liquid  (Ex.  39)  is  a  solution 
of  cochineal  in  water. 

Water  also  dissolves  copper  sulphate  (Ex.  40),  and  the 
solution  is  blue. 

Salt  is  also  soluble  in  water;  but  its  solution,  brine,  is 
without  color.  A  vast  number  of  other  solids  are  more  or 
less  soluble  in  water.  Some  of  them  give  it  color ;  others 
give  no  visible  sign  of  their  presence.  The  most  colorless 
water  may  hold  many  and  a  great  deal  of  these  soluble 
bodies.  They  arc  its  impurities.  And  all  water  that  has 


CHEMISTRY    OF    WATER.  59 

been  in  contact  with  soil  and  rock  holds  more  or  less  of 
these  impurities. 

Gases  also  are  soluble  in  water.  Hydrochloric  acid  gas 
dissolves  in  large  quantity  (Ex.  41)  ;  100  cc.  of  water  will 
take  up  45,000  cc.  of  this  gas  at  a  temperature  of  15°  C., — 
more  if  it  be  colder  and  less  if  it  be  warmer.  Hydrogen  is 
slightly  soluble  in  water,  oxygen  a  little  more  so ;  100  cc. 
of  water  will  take  only  about  3  cc.  of  oxygen.  Water  ab- 
sorbs the  gases  of  the  atmosphere.  These  also  are  impuri- 
ties in  all  natural  water. 

Mineral  Waters.  —  When  water  holds  enough  of  any 
one  thing  in  solution  to  give  it  a  peculiar  taste  it  is  called 
mineral  water.  Such  a  water  receives  the  name  of  the 
substance  in  it,  and  so  does  the  spring  from  which  the 
water  issues.  Sometimes  a  spring  yields  water  in  which 
compounds  of  iron  are  dissolved ;  it  is  then  called  an  iron 
spring,  or  a  clialybeate  spring.  Sometimes  the  compounds 
of  sulphur  are  present  in  large  quantity ;  the  water  is  then 
a  sulphur-water. 

When  water  holds  much  lime  or  magnesia  compounds  in 
solution  it  is  called  hard  water  ;  when  nearly  free  from 
these  it  is  called  soft  water. 

Drinking- Water.  —  Good  water  for  household  use  always 
contains  air  in  solution.  On  standing  quietly  in  a  warm 
place  a  vessel  of  water  will  show  bubbles  of  air  clinging  to 
the  inside  surface.  Try  it.  This  air  if  pure  is  not  only 
wholesome  but  helps  to  make  the  water  palatable.  But 
water  will  absorb  bad  gases  as  freely  as  the  good ;  drinking- 
water  should  not  be  allowed  to  stand  in  bad  air. 

Water  which  holds  a  small  quantity  of  mineral  matter  in 
solution  is  also  wholesome,  but  never  when  it  contains  ani- 
mal substances.  Typhoid  fever,  diphtheria,  and  some  other 
diseases,  are  frequent  where  the  Avater  used  in  households 
is  charged  with  even  very  small  quantities  of  animal  sub- 
stances. 


60  CHEMISTRY    OF    WATER. 

Vegetable  matter  is  less  dangerous  than  animal  matter, 
but  when  much  is  present  it  likewise  makes  the  water  unfit 
for  household  purposes. 

Water  which  holds  fine  particles,  whose  impurities  are 
in  the  form  of  sediment,  may  be  purified  by  filtration.  On 
a  large  scale,  the  water  for  cities  is  filtered  through  beds 
of  sand  and  gravel. 

But  the  most  deadly  impurities  of  water  are  often  in 
solution,  and  these  no  such  filter  can  take  out.  Charcoal- 
filters  may  remove  small  portions,  but  they  cannot  be 
trusted  to  purify  bad  waters  for  household  use. 

Distillation.  —  Pure  water  can  be  obtained  by  boiling 
common  water  and  catching  the  steam  in  a  cold  vessel. 
This  process  is  called  distillation. 

Ex.  Jf2.  —  I  place  50  cc.  of  water  in  my  side-neck  flask 
and  close   it   with  a  cork   through 
which  I  have  pushed  the  stem  of  a 
thermometer,  as   shown  in  Fig.  30. 
To  the  side-neck  I  join  a  long  glass 
tube  by  slipping  a  short   piece   of 
rubber  tube  over  the  end  of  each. 
I  put  the  end  of 
the   glass  tube 
down  into  a  test- 
tube,  which  I  lay 
in   the   water-pan 
nearly  filled  with 
Fig-  30-  cold    water,     and 

finally  I  heat  the  flask  with  a  Bunsen  lamp. 

Note  every  effect  you  can  see  while  the  water  is  being 
heated. 

Keep  watch  of  the  mercury  in.  the  thermometer  before 
the  water  boils. 


CHEMISTRY    OF    WATER. 


61 


Keep  watch  of  the  mercury  in  the  thermometer  after  the 
water  boils.  Note  the  temperature. 

What  happens  in  the  test-tube  ? 

The  Pacts.  — Long  before  water  boils  bubbles  may  be 
seen  escaping  from  it;  these  are  bubbles  of  air  which  was 
in  solution.  Afterward  the  water  boils  and  the  steam  goes 
over  into  the  test-tube,  where  it  is  at  once  changed  back 
into  water  by  cold.  But  it  is  only  the  water  which  goes 
over  as  steam ;  the  solid  impurities  stay  in  solution  in  the 
flask  because  they  need  so  much  more  heat  than  water  does 


Fig.  31. 

to  change  them  into  vapor.  The  water  in  the  tube  is  nearly 
pure;  it  is  called  "distilled  water."  And  this  way  to 
purify  a  liquid  is  called  distillation. 

The  thermometer  shows  that  in  this  process  the  water 
becomes  hotter  and  hotter  until  it  boils,  but  not  afterward. 
When  the  thermometer  marks  100°  C.  it  goes  no  higher, 
though  the  water  boil  never  so  hard.  This  temperature  is 
called  the  boiling-point  of  water.  On  a  Fahrenheit  ther- 


62 


CHEMISTRY    OF    WATER. 


mometer  this  point  is  marked  212°.     Other  liquids  also  are 
purified  by  distillation. 

Fig.  31  shows  a  complete  apparatus,  used  by  chemists, 
for  the  distillation  of  liquids.  The  liquid  is  boiled  in  the 
flask.  Its  vapor  goes  through  the  inside  tube  of  the  con- 
denser c,  while  .the  larger  tube  outside  it  is  kept  full  of 
cold  water.  Here  the  vapor  is  changed  back  to  liquid 


Fig.  32. 

and  this  liquid  drops  into  the  receiver  R.  Rubber  tubes 
carry  the  cold  water  to  and  from  the  condenser  c.  A  ther- 
mometer, t,  may  be  used  to  show  the  boiling-point  of  the 
liquid. 

Effects   of   Cold.  —  A  given  weight  of  water,  say  10  g., 
will  grow  smaller  and  smaller  as  we  make  it  colder.     Its 


CHEMISTRY    OF    WATEK.  63 

volume  will  be  less  and  less  until  its  temperature  is  4°  C. 
But  if  we  cool  it  below  this  point  the  water  will  expand. 
Its  volume  will  then  become  greater  and  greater  quite 
regularly  until  it  is  cooled  down  to  0°  C.  At  0°  the  water 
suddenly  expands  much  more,  and  at  the  same  time  it 
begins  to  freeze.  This  temperature  at  which  water  freezes 
is  called  the  freezing-point  of  water.  It  is  0°  C.  or  32°  F. 

Ice  is  crystallized  water.  In  blocks  of  ice  the  crystals 
are  so  crowded  together  that  their  forms  are  lost.  The 
shapes  of  ice-crystals  are  seen  in  the  beautiful  frost-figures 
on  the  window-pane  in  winter  and  in  snow-flakes,  some  of 
whose  curious  forms  are  shown  in  Fig.  32. 

EXERCISES. 

1.  Study  the  effect  of  mixing  snoiv  and  salt. 

Take  snow  or  pounded  ice,  add  salt  gradually,  stirring 
the  two  well  together. 

What  change  takes  place  in  the  two  solids  ? 
Get  the  temperature  of  the  mixture. 

2.  Compare  the  freezing  and  melting  points  of  water. 

1.  Put  a  small  bottle  or  a  test-tube  partly  filled  with 
water  into  the  freezing  mixture  just  made,  and  stir  this 
water  with  the  bulb  of  a  thermometer  carefully  until  it 
begins  to  freeze. 

At  what  temperature  does  the  freezing  begin  ? 
Does  the  temperature  change  afterwards  ? 

2.  Fill  a  wide-mouth  bottle  with  small  pieces  of  ice  and 
let  it  stand.     Afterward  stir  the  ice  about  in  the  water 
and  take  the  temperature  of  the  mixture. 

At  what  temperature  does  the  ice  melt  ? 
Repeat  these  two  experiments  and  decide  whether  they 
show  that  there  is,  or  is  not,  a   difference  between   the 
melting-point  of  ice  and  the  freezing-point  of  water. 


64  CHEMISTRY    OF    WATER. 

3.  Find  the  boiling-point  of  alcohol.  Fig.  30. 

4.  Find  the  boiling-point  of  a  mixture  of  alcohol  and  water 

made  in  the  proportion  of  one  volume  of  alcohol  to 
two  volumes  of  water. 

Use  the  apparatus  shown  in  Fig.  30. 

Note  the  temperature  when  the  boiling  begins. 

Turn  the  lamp  low  and  let  the  boiling  go  on  slowly 
until  about  5  cc.  of  distillate  is  caught.  Then  change  the 
test-tube. 

Note  the  boiling-point  again. 

Repeat  this  several  times,  and  then  compare  the  distil- 
lates, by  their  odors  and  by  means  of  a  match-flame. 

Which  contains  the  most  alcohol  ? 

Does  the  liquid  in  the  flask  still  contain  alcohol  ? 

The  fact  is  that  two  liquids  which  have  not  the  same 
boiling-point  can  be  roughly  separated  by  this  process  of 
distillation.  It  is  called  fractional  distillation. 

5.  Find  by  evaporation,  whether  the  water  in  use  holds  any 

solid  matter  in  solution. 

How,  by  the  use  of  the  balance  and  the  graduated  cylin- 
der, can  you  find  how  much  of  this  mineral  substance  the 
water  contains? 


CHEMISTRY     OF    THE    ATMOSPHERE. 

NOT  one  hundred  years  ago  the  air  was  thought  to  be  an 
element ;  that  it  is  not  was  proved  by  the  great  French 
chemist  Lavoisier. 

Lavoisier's  Experiment.  — The  apparatus  which  he  used 
was  much  like  that  shown  in  Fig.  33.  A  small  quantity  of 
pure  mercury  was  put  into  a  flask  which  was  placed  over 
a  furnace.  The  flask  had  a  long,  slender  neck,  which 


Fig.  33. 

reached  over  into  a  pan  of  mercury.  Standing  mouth 
downward  in  this  pan  was  a  jar  filled  with  air,  and  the 
neck  of  the  flask  was  bent  up  into  it. 

When  all  was  ready,  Lavoisier  lighted  the  fire  in  the 
furnace  and  kept  it  burning  all  the  time  for  twelve  days. 
On  the  second  day  he  saw  little  red  flakes  of  something 
swimming  around  on  the  surface  of  the  mercury.  For  four 
or  five  days  afterward  the  quantity  of  this  red  substance 

65 


f>G  CHEMISTRY    OF    7777?    ATMOSPHERE. 

increased  while  the  quantity  of  air  in  the  receiver  dimin- 
ished. For  some  time  longer  the  heat  was  kept  up,  but  no 
further  change  took  place,  and  this  part  of  the  work  was 
done.  He  had  less  air  in  the  apparatus  than  at  first,  shown 
by  the  mercury  rising  in  the  jar,  but  instead  of  the  air 
which  was  lost  he  had  the  new  red  substance  in  the  flask. 

What  was  this  red  substance?  To  find  out,  Lavoisier 
heated  it  in  a  tube  so  fixed  that  any  gas  which  should  be 
produced  would  be  caught  in  a  vessel  over  mercury.  The 
red  substance  became  black,  then  began  to  waste  away 
while  bubbles  of  a  colorless  gas  were  caught  in  the  vessel 
prepared  for  the  purpose,  and  globules  of  shining  mercury 
gathered  on  the  walls  of  the  tube  above  the  heated  part. 
What  was  the  colorless  gas  ?  Lavoisier  plunged  a  candle- 
flame  into  it;  the  candle  burned  with  a  dazzling  light. 
The  gas  was  oxygen. 

But  whence  came  this  oxygen  to  combine  with  the  mer- 
cury when  it  was  heated  with  air  in  Lavoisier's  flask  ?  The 
air  must  have  given  it  to  the  mercury,  and  so  the  experi- 
ment proved  that  oxygen  is  one  constituent  of  air. 

In  the  flask  and  the  glass  jar  (Fig.  33)  there  was  still  left 
a  large  quantity  of  air-like  substance.  But  on  plunging  a 
candle-flame  into  it  the  flame  was  put  out  as  it  would  have 
been  in  water.  Plainly  it  was  not  air.  In  fact  it  was  the 
gas  called  nitrogen. 

Lavoisier's  experiment  proved  that  oxygen  and  nitrogen 
are  two  constituents  of  air.  There  are  indeed  a  few  other 
gases  in  the  atmosphere  beside  these,  but  in  comparison 
with  these  the  quantity  of  them  is  small.  Oxygen  and 
nitrogen  are  the  two  chief  constituents  of  the  air. 

NITROGEN. 

When  a  substance  burns  in  air  .it  takes  the  oxygen  and 
leaves  the  nitrogen.  Lavoisier  burned  mercury,  but  sul- 


CHEMISTRY    OF    THE    ATMOSPHERE.  67 

phur  and  some  other  things  will  burn  more  quickly,  and 
may  be  used  instead.  Let  us  try  sulphur,  and  afterward 
phosphorus. 

Ex.  43.  —  I  cut  a  slice  half  an  inch  thick  from  a  cork 
which  is  much  smaller  than  the 
mouth  of  my  bottle.  I  shape  the 
top  of  the  cork  into  a  shallow  cup 
and  rub  it  well  with  crayon-powder, 
or  better  with  a  paste  of  moistened 
plaster  of  Paris.  I  put  sulphur  in 
this  cup,  place  the  cup  on  the  shal- 
low water  in  the  water-pan,  set  fire 

to  the  sulphur,  and  put  a  bottle  bottom  upward  over  it,  as 
shown  in  Fig.  34.  Describe 

The  flame  of  the  sulphur. 

The  action  of  the  water  when  the  burning  is  over. 

The  change  in  the  gas  after  long  time  standing. 

Ex.  44.  —  I  use  a  piece  of  phosphorus,  not  larger  than  a 
good-sized  kernel  of  wheat,  with  another  bottle  holding 
about  200  cc.  I  treat  it  just  as  I  did  the  sulphur,  and 
again  describe  the  flame,  the  action  of  the  water  afterward, 
and  the  appearance  of  the  gas  inside  after  standing  some 
time  over  water. 

But  the  handling  of  phosphorus  is  dangerous,  unless  it 
is  done  with  great  care.  Phosphorus  takes  fire  easily  and 
burns  the  flesh  cruelly.  Cut  it  under  water,  lift  the  piece 
with  the  knife-blade,  dry  it  by  gentle  contact  with  filter- 
paper,  and  put  it  into  a  dry  cup.  Never  handle  phosphorus 
without  using  the  greatest  care. 

Ex.  45- — When  the  gas  in  the  bottle  used  in  Ex.  43  has 
become  clear  I  slip  a  square  of  glass  or  of  cardboard  under 
the  mouth  of  the  bottle,  lift  it  out  of  the  water,  turn  it 
mouth  upward,  stand  it  on  the  table  and  leave  it  covered. 


68  CHEMISTRY    OF    THE    ATMOSPHERE. 

I  at  once  ignite  a  match,  uncover  the  bottle,  and  insert 
the  flame ;  the  nitrogen  will  quench  it.  I  leave  the  bottle 
uncovered.  I  treat  the  bottle  used  in  Ex.  44  in  the  same 
way ;  the  nitrogen  again  puts  out  the  flame.  I  leave  this 
bottle,  also,  uncovered. 

Ex.  46-  —  I  now  again  insert  a  match-flame  in  the  bottle 
first  left  uncovered,  and  afterward  in  the  other.  The  flame 
is  not  quenched. 

What  does  this  prove? 

Ex.  47.  —  I  now  add  a  little  blue  litmus-water  to  the 
water  in  the  bottle  in  which  sulphur  was  burned. 

Note  the  change  of  color.     Compare  Ex.  8. 

What  causes  this  change  of  color? 

Ex.  48.  —  I  add  blue  litmus-water  to  the  water  in  the 
second  bottle  which  was  left  uncovered  in  Ex.  45;  it 
changes  from  blue  to  red. 

Can  you  explain  this  change  of  color  ? 

Burning  of  Sulphur Sulphur,  when  burning  with  its 

feeble  blue  flame,  combines  with  oxygen,  and  the  two 
become  sulphur  dioxide.  The  water  soon  dissolves  the 
whitish  vapor  and  rises  into  the  vessel,  and  at  last  fills 
just  the  space  which  the  oxygen  of  the  air  occupied  at 
first,  while  the  nitrogen  of  the  same  air  remains  above  the 
water  (Ex.  43). 

The  sulphur  dioxide  shows  its  presence  in  the  water  by 
reddening  the  blue  litmus,  Ex.  47,  as  it  did  in  Ex.  8. 

Burning  of  Phosphorus.  —  When  phosphorus  is  used 
the  action  is  much  the  same.  It  combines  with  the  oxy- 
gen of  the  air  and  forms  phosphoric  oxide,  which  fills  the 
vessel  as  a  milk-white  vapor.  Water  soon  dissolves  this 
oxide,  and  the  nitrogen  of  the  air  is  left  as  before. 

The  phosphoric  oxide  also  shows  its  presence  in  the  water 
by  reddening  blue  litmus  (Ex.  48). 


CHEMISTRY    OF    THE   ATMOSPHERE.  69 

Properties  of  Nitrogen Nitrogen  is  a  colorless  gas 

(Exs.  43,  44).  It  is  lighter  than  air  (Ex.  46),  but  a  liter  of 
it  weighs  fourteen  times  as  much  as  a  liter  of  hydrogen. 
It  will  quench  fire  (Ex.  45),  because  it  cannot  unite  with 
the  elements  of  the  fuel  as  oxygen  does.  In  fact,  nitro- 
gen is  the  least  active  of  the  elements.  It  will  not  only 
quench  fire,  but  if  breathed  instead  of  air  it  will  quench 
life  also.  Yet  it  cannot  be  poisonous,  since  we  inhale  it 
with  every  breath  without  injury.  It  is  the  oxygen  of  the 
air  that  sustains  life,  and  it  is  the  absence  of  oxygen,  and 
not  the  presence  of  nitrogen,  which  causes  death  when  pure 
nitrogen  is  breathed. 

Other  Constituents  of  Air.  —  The  air  also  contains 
water  in  form  of  invisible  vapor.  This  is  proved  by  placing 
a  piece  of  caustic  potash  in  an  open  dish.  The  potash 
will  very  soon  become  wet,  and  if  left  for  some  time  it 
will  be  dissolved  by  the  water  which  it  takes  from  the  air. 
Try  it.  The  moisture  to  be  seen  on  the  outside  of  a  vessel 
of  ice-water  in  summer  is  the  condensed  water-vapor  of  the 
air.  Dew  and  hoar-frost  are  also  the  water  of  the  air, 
changed  by  cold  from  vapor  to  liquid  and  solid  forms. 

The  air  also  contains  carbon  dioxide.  This  is  shown  by 
lime-water,  which  if  left  exposed  in  an  open  vessel  will 
become  covered  in  a  few  hours  with  a  white  crust.  Try  it. 
This  crust  is  the  same  substance  which  is  seen  in  lime- 
water  after  it  has  received  carbon  dioxide  (Ex.  7). 

The  air  also  contains  ammonia  in  very  small  quantities. 

Nitrogen,  oxygen,  water-vapor,  carbon  dioxide,  and  am. 
monia  are  the  regular  constituents  of  the  atmosphere.  Our 
next  question  is,  How  much  of  each  of  these  substances  is 
to  be  found  in  air  ? 

The  Analysis  of  Air.  —  We  set  out  now  to  find  how 
many  cubic  centimeters  of  nitrogen  and  how  many  of  oxy- 
gen and  carbon  dioxide  there  are  in  100  cc.  of  air. 


70 


CHEMISTRY    OF    THE    ATMOSPHERE. 


To  do  this  we  will  imprison  a  vesselful  of  air,  and  then 
run  into  it  a  liquid  which  will  absorb  both  the  oxygen  and 
the  carbon  dioxide  completely,  and  leave  the  nitrogen.  We 
can  then  measure  the  nitrogen  which  is  left,  and  we  can 
find  out  how  much  there  was  of  the  other  two,  by  measur- 
ing the  liquid  which  has  gone  into  the  tube  to  take  their 
place. 

Ex.  49-  —  OUR  APPARATUS.  —  I  take  a  test-tube,  t  (Fig. 
35)  to  hold  the  air.     A  six-inch  tube,  f  inch  in 
j    diameter,  will  do;  an  eight-inch  tube  of  the  same 
\|       diameter  is  better.     The  rubber  stopper,  c,  is  so 
large  that  its  small  end  will  enter  the  tube  only 
about  a  half-inch.     It   has  two  holes ;    to  close 

fone  I  have  a  solid  rod  of  glass,  s  ;  for  the  other, 
a  glass  tube  reaching  just  a  very  little  below  the 
cork,  as  shown.     A  piece  of  thin  rubber  tubing, 
&,        A,  is  cut  about  six  inches  long.     There  is  a  pinch- 
fp*      cock,  p,  by  which  its  walls  may  be  pinched  so  as 
Fi«.  35.       £0  c]ose  ft  completely.     F  is  a  small  glass  funnel. 
The  lower  end  of  h  I  stretch  over 
the  tube  in  the  cork  c,  and  its  upper 
end  I  fix  over  the  stem  of  F,  and  then 
I  place  the  funnel  in  the  clamp  of  the 
support,  as  shown  in  Fig.  36,  and  re- 
move the  rod  s. 

THE  LIQUID.  —  To  absorb  the  oxy- 
gen and  carbon  dioxide  gases  I  use 
a  mixture  of  pyrogallic  acid  and  po- 
tassium hydrate. 

I  take  a   small  teaspoonful  of  the 
solid   acid   and   pour   on  it  10  cc.  of 
water ;  it  will  soon  dissolve.     To  this 
I  then  add  5  cc.  of  strong  solution  of  potassium  hydrate, 
and  at  once  pour  it  into  the  funnel.     Next,  I  hold  the  dish 


Fig.  36. 


CHEMISTRY    OF    THE    ATMOSPHERE. 


71 


Fig.  37. 


below  the  cork  and  open  the   pinch-cock  p  a  moment,  to 

let  the  liquid  run  down  and  fill  the  tubes  completely.     I 

carefully  take  off  the  drop,  which  hangs 

at  the  lower  end  of  the  tube  below  the 

cork,  with  a  piece  of  filter-paper. 

I  press  the  tube  t  up  over  the  cork 

until  the  joint  is  air-tight,  as  seen  in 

Fig.  37,  and   after  a  minute  I  put  the 

rod  s  into  the  open  hole  of  the   cork. 

I  have  now  imprisoned  a  tubeful  of  air ; 

none   can   get   out,    and   no    more    can 

get  in. 

I  left  the  hole  in  the  cork  open,  be- 
cause if  it  were  not  open  the  pressure 

of  the  cork  would  crowd  the  air  below, 

and  there  would  be  too   much   in   the 

tube;  and  then,  too,  handling  the  tube  warmed  it,  and  the 
volume  of  air  changes  with  heat. 
With  the  hole  open,  the  air  in  the 
tube  soon  comes  to  be  just  as  warm 
and  just  as  much  pressed  as  the  air 
outside.  Whenever  a  gas  of  any  kind 
is  to  be  measured  its  temperature  and 
pressure  must  be  the  same  as  those  of 
the  air  outside. 

THE  ABSORPTION.  —  I  now  press 
the  pinch-cock  p ;  a  little  stream  of 
the  liquid  falls  into  t  at  once,  and 
then  drops  follow,  or,  if  the  tube  be 
slightly  inclined,  a  slender  stream  will 
flow  down  its  side.  It  will  continue 
to  enter  as  long  as  there  is  any  oxy- 
gen or  carbon  dioxide  for  it  to  absorb,  and  then  stop. 

The  gas  which  is  left  in  the  tube  is  nitrogen. 


Fig.  38. 


72  CHEMISTRY    OF    THE    ATMOSPHERE. 

But  this  gas  is  crowded  down  by  the  pressure  of  the 
liquid  in  the  rubber  tube  and  funnel  above,  and  so  I  take 
hold  of  the  cork  c,  and  the  rim  of  t,  not  to  warm  the  gas 
with  my  hand,  and  lift  the  tube  bottom  up,  as  shown  at 
T  in  Fig.  38,  making  the  level  of  the  liquid  the  same  in 
the  tube  and  in  the  funnel.  I  then  open  the  pinch-cock. 
Some  of  the  liquid  will  run  out  of  T.  When  the  liquid 
stands  at  the  same  level  in  the  tube  and  in  the  funnel,  I 
close  the  cock  and  bring  the  tube  down  again. 

The  almost  black  liquid  in  t  has  now  taken  out  all  the 
oxygen  and  carbon  dioxide  from  the  tubeful  of  air,  and 
left  all  its  nitrogen. 

THE  MEASURING.  —  I  must  measure  the  liquid  in  the 
tube  to  find  how  much  oxygen  was  taken  out,1  and  the 
space  above  it  to  find  how  much  nitrogen  was  left. 

To  do  this  I  slip  two  small  rubber  rings  up  on  the  tube, 
and  make  the  upper  edge  of  one  mark  the  place  of  the 
lower  end  of  the  cork,  and  of  the  other,  the  top  of  the 
liquid.  These  rings  must  not  afterward  be  disturbed. 

I  may  now  remove  the  cork,  empty  the  tube,  rinse  it 
with  water,  and  then  let  the  last  drop  of  water  drain  away. 
Finally,  I  use  my  graduated  cylinder  to  find  out  exactly 

How  many  cc.  water  will  fill  the  tube  to  the  first  ring. 

How  many  cc.  water  will  fill  the  tube  from  the  first  to 
the  second  ring. 

THE  CALCULATIONS.  —  From  these  two  numbers  we  can 
find  what  part  of  the  air  is  nitrogen  and  what  part  is 
oxygen.  For  they  help  us  to  answer  the  following 
questions,  in  their  order,  one  after  another,  as  shown 
by  an  example  below. 

1  And  carbon  dioxide  also.  But  the  volume  of  the  carbon  dioxide, 
in  so  small  a  quantity  of  air  as  we  use,  is  so  little  that  we  cannot 
measure  it  with  our  apparatus.  We. may  leave  it  out  of  account  in 
this  experiment. 


CHEMISTRY    OF    THE    ATMOSPHERE.  73 

How  many  cc.  of  air  were  in  the  tube  at  first? 
How  many  cc.  of  nitrogen  did  this  air  yield  ? 
How  many  cc.  of  oxygen  did  the  same  air  yield? 
Then  what  fractional  part  of  the  air  is  nitrogen? 
What  fractional  part  of  the  air  is  oxygen  ? 
And  how  many  cc.  nitrogen  in  100  cc.  of  air  ? 
How  many  cc.  of  oxygen  in  100  cc.  of  air  ? 

An  Example.  —  In  an  actual  experiment  it  was  found 
to  take  of 

Water  to  fill  the  tube  to  the  first  ring 6.0  cc. 

Water  to  fill  the  tube  from  the  first  to  second  ring .      23.5  cc. 

Hence  the  number  of  cc.  of  air  taken 29.5  cc. 

And  the  number  of  cc.  of  nitrogen  found    ....      23.5  cc. 
And  the  number  of  cc.  of  oxygen  found      ....        6.0  cc. 

Now  this  would  show  plainly  that  f  $g  of  the  air  is  nitro- 
gen and  2%%  of  it  is  oxygen.  Then  in  100  cc.  of  air  there 
would  be 

Nitrogen 79.66  cc. 

Oxygen 20.34  cc. 

The  Exact  Composition  of  Air Some  of  the  great- 
est chemists  have  devoted  much  time  to  find  out  exactly 
how  much  oxygen  and  nitrogen  the  air  contains.  The}' 
have  used  other  methods,  more  accurate  than  that  of  al> 
sorption,  and  apparatus  much  more  refined  than  that  which 
has  answered  our  purpose.1  They  have  found  the  per- 
centage composition  to  be 

Nitrogen 79.04 

Oxygen 20.96 

Air 100.00 

1  For  full  description,  see  Roscoe  and  Schorleinmer,  Vol.  I.  pp. 
439-447. 


74  CHEMISTRY    OF    THE   ATMOSPHERE. 

When  the  gases  are  weighed  instead  of  being  measured 
the  numbers  are  different.  Thus : 

Nitrogen 77.00 

Oxygen 23.00 

Air 100.00 

How  much  Water-vapor  in  Air?  —  The  quantity  of 
water-vapor  in  the  air  is  all  the  time  changing.  There  is 
only  a  certain  amount  which  air  can  hold  at  any  given 
temperature,  and  the  only  way  to  make  it  able  to  take 
any  more  is  to  heat  it. 

But  the  atmosphere  seldom  has  all  that  it  can  hold. 
At  60°  F.  the  quantity  will  be  usually  found  between  ^ 
and  ?fo  of  the  bulk  of  the  air. 

"What  Fraction  of  the  Air  is  Carbon  dioxide?  — 
Sometimes  as  much  as  y^^  of  the  air  is  carbon  dioxide;  at 
other  times  or  places  there  may  be  no  more  than  5^0  0. 
Perhaps  the  average  proportion  may  be  55^- 

So  small  a  quantity  as  one  cubic  inch  of  this  gas  in 
twenty-five  hundred  cubic  inches  of  air  seems,  at  first 
thought,  too  small  to  be  worthy  of  notice.  It  is  not  so. 
Carbon  dioxide,  little  as  there  is  of  it,  is  one  of  the  most 
important  substances  in  the  atmosphere.  Plants  cannot 
grow  without  it.  It  is  a  needful  part  of  their  food,  and 
they  are,  when  growing,  all  the  time  taking  it  out  of  the 
atmosphere.  It  is  returned  to  the  air  by  the  breathing  of 
animals,  by  the  burning  of  fuels,  by  the  decay  of  plants, 
and  by  volcanos. 

We  will  shortly  make  a  special  study  of  this  gas,  but  for 
the  present  we  go  on  with  the  description  of  air. 

The  Atmosphere  a  Mixture  or  a  Compound  ? —  It  is 
found  that  the  carbon  dioxide  of  the  air  makes  lime- 
water  turbid  just  as  the  same  gas  from  marble  will  do.  The 
water-vapor  in  the  air  may  be  condensed  to  liquid  by  cold, 


CHEMISTRY    OF    THE    ATMOSPHERE.  75 

just  as  water-vapor  alone  may  be.  Bodies  burn  in  oxygen ; 
they  burn  also  in  air,  of  which  oxygen  is  a  constituent 
Nitrogen  alone  extinguishes  fire  completely,  and  nitrogen 
in  the  air  strives  to  do  so,  but  succeeds  only  in  making 
them  burn  more  feebly  in  the  oxygen  which  is  present. 
In  fact,  the  properties  of  the  constituents  of  air  can  be 
easily  detected  in  the  atmosphere  itself. 

But  when  substances  combine  they  form  a  compound  in 
which  their  own  properties  are  not  to  be  found.  We 
therefore  say  that  the  atmosphere  is  not  a  compound,  but 
a  mixture. 

Constant  and  Uniform  in  Composition The  pro- 
portions of  oxygen,  nitrogen,  and  carbon  dioxide  are  always 
very  nearly  the  same.  Air  on  the  tops  of  mountains,  and 
in  the  low  places  of  the  earth,  and  in  different  countries, 
have  all  these  constituents,  and  very  nearly  the  same  rela- 
tive quantities  of  them. 

The  heavy  carbon  dioxide,  the  lighter  oxygen,  and  the 
still  lighter  nitrogen,  are  uniformly  mixed  together.  Why 
do  they  not  separate  into  layers,  as  water  and  oil  would  do 
after  having  been  mixed  never  so  perfectly? 

Diffusion  of  Gases The  fact  is  that  gases  will  not 

stay  unmixed  if  they  touch  each  other.  We 
may  bring  a  light  gas  on  top  of  a  heavy  one, 
and  find  that  a  part  of  the  light  one  will 
sink,  and  a  part  of  the  heavy  one  will  rise, 
until  the  two  are  completely  mixed. 

Ex.  50.  —  I  will  bring  hydrogen  to  rest  on 
top  of  air.     I  select  two  wide-mouth  bottles, 
each  holding  about  200  cc.,  one  with  a  neck 
a  little  smaller  than  that  of  the  other,   so          Fig-  39- 
that  they  may  be  put  together,  as  in  Fig.  39.     The  upper 
bottle  is  to  be  filled  with  hydrogen,  the  lower  one  with  air. 

To  FILL  THE  BOTTLE  WITH  HYDROGEN.  —  I  first  fill  it  to 


76  CHEMISTRY    OF    THE    ATMOSPHERE. 

the  brim  with  water ;  cut  a  piece  of  heavy  blotting-paper  a 
little  larger  than  its  mouth  and  slide  it  on  as  a  cover  and 
smooth  it  down  closely  upon  the  glass  (Fig.  40,  a).  I  grasp 
the  bottle  and  turn  it  bottom  upward  over  the  pan,  B, 
lower  it  into  the  water,  remove  the  paper  cover,  and 
stand  the  bottle  bottom  upward  in  the  water.  The  press- 
ure of  the  atmosphere  will  safely  hold  the  water  in  the 
bottle  while  I  invert  it,  and  while  its  mouth  is  under  water 
in  the  pan. 

I  now  put  a  few  clippings  of  zinc  into  a  side-neck  flask 
and   fix  the   flask   in   the   clamp,  then  join  one  end  of  a 


Fig.  40. 

rubber  tube  to  the  side-neck,  the  other  to  a  glass  tube 
which  reaches  into  the  water  of  the  pan.  I  pour  some 
dilute  hydrochloric  acid  (half  water)  into  the  flask  and  cork 
the  neck  at  once.  As  soon  as  the  air  is  driven  out  of  the 
flask  I  put  the  end  of  the  glass  tube  under  the  mouth  of 
the  bottle,1  and  collect  the  hydrogen  as  shown  in  Fig.  40. 

1  A  little  shelf  for  the  bottle  to  stand  on  may  be  made  by  bending 
the  ends  of  a  strip  of  sheet-iron  down  to  serve  as  feet  to  stand  on  the 
bottom  of  the  water-pan. 


CHEMISTRY    OF    THE    ATMOSPHERE.  77 

When  the  bottle  is  filled  with  gas  I  again  slide  the  cover 
of  blotting-paper  under  its  mouth,  and  hold  it  there  while 
I  lift  this  bottle  arid  carry  it  over  the  mouth  of  the  other. 
I  then  remove  the  paper,  and  at  once  let  the  mouth  of  this 
hydrogen-bottle  down  into  that  of  the  air-bottle,  as  shown 
in  Fig.  39. 

After  waiting  ten  minutes  I  lift  the  two  bottles,  hold 
them  over  the  water-pan,  then  separate  them,  and  quickly 
put  them  both,  mouth  down,  in  the  water. 

With  a  lighted  match  in  one  hand,  I  lift  the  hydrogen- 
bottle  and  bring  the  flame  to  its  mouth ;  a  small  explosion 
follows.  I  treat  the  air-bottle  in  the  same  way ;  there 
is  another  explosion.  These  explosions  show  that  there 
was  a  mixture  of  hydrogen  and  air  in  each  bottle. 

Now  air  is  almost  14.5  times  heavier  than  hydrogen,  and 
yet,  to  make  that  mixture,  it  must  have  risen  into  tho 
upper  bottle  while  the  lighter  hydrogen  must  have  fallen 
into  the  lower  one.  They  have  mixed  in  spite  of  their 
difference  in  weight. 

This  mingling  of  gases,  when  they  are  simply  brought 
into  contact  with  one  another,  is  called  the  diffusion  of 
gases.  The  difference  in  weight  of  oxygen,  nitrogen,  and 
carbon  dioxide  would  arrange  these  gases  in  layers  one 
above  another,  the  heaviest  at  the  bottom,  but  the  principle 
of  diffusion  will  not  allow  this  separation ;  it  causes  all 
these  gases  to  mix  uniformly  in  every  part  of  the  atmos- 
phere. 

RESPIRATION. 

Animals  and  plants  need  the  gases  of  the  atmosphere  as 
much  as  they  need  food  and  soil.  Without  food,  an  ani- 
mal starves ;  without  air,  its  death  would  come  still  more 
quickly.  Pluck  its  roots  from  the  soil,  and  a  plant  withers 
and  dies ;  give  it  the  most  fertile  soil,  but  take  away  the 
air,  and  its  death  is  just  as  certain. 


78  CHEMISTRY    OF    THE   ATMOSPHERE. 

Both  animals  and  plants  are  able  to  take  the  air  into 
their  bodies  and  then  throw  it  out  again.  This  act  is  called 
respiration. 

Respiration  of  Animals.  — When  an  animal  breathes, 
the  air  which  goes  to  the  lungs  contains  oxygen  and  nitro* 
gen,  with  a  little  of  carbon  dioxide,  water-vapor,  and  still 
less  of  a  few  other  gases. 

But  what  comes  from  the  lungs  ?  Large  quantities  of 
water-vapor,  as  we  know  by  observation,  as  in  a  cold  Avinter 
morning,  when  every  breath  looks  like  a  cloud  of  steam. 
We  see  the  moisture  of  the  breath  at  such  times,  because 
the  cold  air  condenses  it  and  makes  it  visible. 

But  we  can  find  this  water,  and  something  else,  at  the 
same  time  by  experiment. 

Ex.  51.  —  I  take  a  clean  and  dry  bottle,  cover  the  lower 
half  of  its  mouth  with  my  open  lips  while  I  pass  a  full 
breath  into  it.  Notice  the  deposit  of  dew  on  the  walls  of 
the  bottle. 

I  next  pour  a  few  cubic  centimeters  of  lime-water  into 
the  bottle  and  rinse  the  walls  with  it,  and  note  the  effect 
on  the  lime-water. 

Ex.  52.  —  I  pour  25  cc.  strong  lime-water  into  a  clean 
bottle  and  add  25  cc.  of  water.  I  take  a  glass  tube,  or  a 
straw,  and,  with  one  end  in  my  mouth,  the  other  in  the 
lime-water,  I  breathe  through  the  transparent  liquid  per- 
haps two  or  three  times. 

What  is  the  effect  on  the  lime-water  ? 

What  two  substances  have  we  found  which  must  have 
been  thrown  out  in  the  breath  ? 

Now,  besides  the  carbon  dioxide  and  water,  which  we 
detect  by  these  experiments,  there  is  the  nitrogen.  The 
fact  is  that  while  the  nitrogen  of  the  air  is  returned  to  the 
air  by  the  breath,  the  oxygen  is  used  up  in  the  body  to 
make  carbon  dioxide  and  water. 


CHEMISTRY    OF    THE   ATMOSPHERE.  79 

How  is  THIS  BROUGHT  ABOUT  ?  —  The  air  goes  into  the 
lungs,  and  its  oxygen  passes  through  the  pores  of  the 
delicate  membrane,  of  which  the  lungs  are  made,  into  the 
blood.  With  the  blood,  as  it  goes  from  the  lungs,  this  oxy- 
gen is  carried  to  every  part  of  the  whole  body.  It  is  while 
in  the  blood,  going  from  place  to  place,  that  the  oxygen 
meets  the  hydrogen  and  the  carbon. 

But  how  came  these  to  be  in  the  blood  ?  Every  part 
of  our  bodies  is  constantly  wearing  out.  You  cannot  move 
a  filler  without  some  of  its  particles  being  worn  away. 
You  cannot  step  without  some  of  the  particles  of  the  legs 
be:ng  worn  out.  Every  breath,  every  motion,  every  thought, 
renders  useless  some  portions  of  the  parts  of  the  body 
which  aro  acting  at  the  time. 

These  worn-out  particles  are  all  the  time  going  into  the 
blood.  They  consist  chiefly  of  hydrogen  and  carbon,  and  it 
is  from  these  worn-out  particles  of  our  bodies  that  the  oxy- 
gen gets  hydrogen  and  carbon  to  form  the  water-vapor  and 
the  carbon  dioxide  which  are  thrown  out  at  every  breath. 

Life  itself  depends  upon  this  process.  These  waste  par- 
ticles are  the  impurities  of  the  blood,  and  they  must  be 
taken  out  or  death  will  quickly  come.  As  long  as  oxygen 
is  regularly  supplied  to  the  lungs  it  will  change  these  im- 
purities into  water  and  carbon  dioxide,  and  in  these  forms 
they  will  be  thrown  out  in  the  breath. 

These  two  seem  to  be  the  most  abundant  substances 
thrown  out,  but  they  are  by  no  means  the  only  ones.  Many 
other  impurities  are  exhaled  at  the  same  time.  Some  of 
these  are  very  offensive,  and  all  of  them  are  very  injur- 
ious to  health  if  taken  again  into  the  lungs. 

Air  spoiled  by  breathing Oxygen  is  the  only  thing 

in  the  air  that  can  purify  the  blood,  and  this  element  is 
being  taken  from  it  by  every  breath.  Once  breathed,  the 
air  is  unfit,  on  this  account,  to  be  breathed  again. 


80  CHEMISTRY    OF    THE   ATMOSPHERE. 

This  is  only  one  way,  and  that  not  the  worst,  in  which 
the  act  of  breathing  spoils  the  air.  Every  breath  is  pol- 
luting all  the  air  into  which  it  is  thrown,  with  the  impuri- 
ties of  the  blood.  Air  without  its  oxygen  would  not  be 
poisonous  nor  filthy,  but  air,  with  the  abundant  impurities 
thrown  into  it  with  the  breath,  is  both  poisonous  and 
filthy.  Were  we  able  to  see  the  impurities  of  air  which 
has  been  breathed,  we  would  shun  such  atmosphere  as  we 
now  shun  the  water  of  a  stagnant  pool.  Ought  we  to 
shun  it  less  because  they  are  invisible?  ,  .^ 

Ventilation.  —  It  is  necessary  to  change  the  air  in  the 
rooms  of  our  houses  very  often  and  very  thoroughly,  in 
order  to  avoid  being  poisoned  by  our  own  breath. 

The  removal  of  foul  air  and  the  introduction  of  that 
which  is  pure  is  called  ventilation.  Every  room  in  which 
human  beings  are  expected  to  live  ought  to  have  some 
means  of  ventilation. 

Our  chemistry  teaches  us  these  facts,  but  chemistry  is 
not  left  to  do  this  alone.  The  same  lesson  is  taught  by 
some  of  the  most  awful  experiences. 

Sometime  more  than  a  hundred  years  ago  it  happened 
that,  in  Calcutta,  one  hundred  and  forty-six  persons  were 
shut  up  for  a  night  in  a  small  room  called  the  Black  Hole. 
At  dawn  of  day  only  twenty-three  remained  alive. 

The  passengers  on  board  a  ship  were  all  crowded  into 
the  cabin,  one  stormy  night.  One  hundred  and  fifty  went 
in,  but  only  eighty  came  out  alive. 

Examples  of  less  painful  kind  are  much  more  common. 
A  schoolroom  is  unventilated ;  the  pupils  become  listless 
and  dull  from  the  influence  of  bad  air.  A  church  or  hall 
is  not  ventilated,  and  a  large  audience  becomes  languid 
and  sleepy.  A  bedroom  has  its  doors  and  windows  tightly 
shut;  the  sleeper  awakes  in  the  morning  unrested  and 
with  headache. 


CHEMISTRY    OF    THE    ATMOSPHERE.  81 

These  are  the  effects  of  breathing  air  which  has  already 
been  breathed. 

Every  building  in  which  people  are  to  live,  even  for 
short  times,  ought  to  have  the  means  of  ventilation  "built 
in,"  but  if  the  builder  of  the  house  has  not  provided  some 
special  means,  then  the  windows  and  doors  should  be  freely 
used  for  the  purpose.  There  should  be  two  openings  in 
every  inhabited  room,  one  near  the  top,  the  other  near  the 
bottom.  Out  of  one  of  these  the  foul  air  may  escape  while 
fresh  air  may  come  into  the  room  through  the  other.  A 
window  let  down  a  little  from  the  top,  and  raised  a  little 
from  the  bottom,  will  meet  this  condition  in  a  degree. 

The  Respiration  of  Plants Plants  breathe.  They 

take  air  into  their  leaves  and  throw  it  back  into  the  atmos- 
phere again ;  and  this  is  respiration. 

The  leaves  are  curiously  made.  Look  at  one  with  a 
good  microscope,  and  we  see  that  its  surface  is  covered 
with  little  openings,  or  pores.  What  a  multitude  of  them  ! 
In  some  cases  more  than  a  hundred  thousand  in  the  small 
space  of  one  square  inch !  They  are  found  on  both  the 
under  and  the  upper  side  of  the  leaf.  The  air  is  taken 
into  these  little  mouths  on  the  under  side,  while  from  those 
on  the  upper  side  the  gases  are  thrown  out. 

Animals  breathe  in  order  to  get  oxygen  from  the  air ; 
plants  breathe  in  order  to  get  water- vapor  and  carbon  diox- 
ide. The  carbon  dioxide  is  decomposed ;  its  carbon  is  kept 
in  the  plant  while  its  oxygen  is  thrown  out.  While  the  sun 
shines  this  action  goes  on ;  in  the  dark  it  does  not,  for  it  is 
found  that,  at  night,  carbon  dioxide  is  thrown  out  instead 
of  oxygen. 

Animals  are  all  the  time  using  up  the  oxygen  of  the 
atmosphere ;  plants  are  by  the  help  of  sunlight  throwing 
it  into  the  atmosphere.  Animals  are  constantly  giving 
water-vapor  and  carbon  dioxide  to  the  atmosphere ;  plants 


82  CHEMISTRY    OF    THE    ATMOSPHERE. 

are  busy  in  taking  these  substances  out.  Thus  do  these 
two  great  kingdoms  of  nature  balance  and  sustain  each 
other. 

EXERCISES. 
1.   Study  the  action  of  sulphuric,  acid  on  oxalic  acid. 

1.  Bring  small  quantities  of  the  two  substances  together 
in  a  test-tube,  using  the  concentrated  sulphuric  acid,  and 
crystals  of  oxalic  acid.     Discover  whether  chemical  action 
will  take  place  in  the   cold,   the  effect   of  heat,  whether 
a  gas  is  set  free,  and  any  other  facts  you  can.     This  work 
will  suggest  the  next  step. 

2.  Proceed  to  collect  some  of  the  gas  in  order  to  learn 
what  it  is.     To  do  this,  put  5  g.  of  oxalic  acid,  in  crystals, 
with  15  cc.  of  strong  sulphuric  acid  into  a  side-neck  flask, 
to  make  the  gas ;    and  to  collect  it,  arrange  two   conical 
flasks  and  one  test-tube,  which  is  fitted  with  a  cork  and 
tubes  in  the  same  manner  as  the  flasks. 

8.  Examine  the  gas.  Put  a  flame  into  the  mouth  of  the 
first  flask  to  learn  whether  the  gas  is  combustible  or  other- 
wise ;  and  for  the  name  of  the  gas  which  gives  the  result 
you  get  here  consult  p.  46. 

Test  the  gas  in  the  second  flask  with  lime-water,  and 
name  the  gas  which  this  test  reveals. 

Having  now  proved  that  the  gas  which  is  set  free  by  the 
action  of  the  two  acids  is  a  mixture  of  carbon  monoxide 
and  carbon  dioxide,  you  can  take  the  fourth  step  in  your 
investigation,  which  is  to 

4.  Analyze  the  mixture.  Do  this  by  the  method  of 
"  absorption,"  the  same  as  that  used  in  the  analysis  of  air 
in  Ex.  49. 

Fill  the  funnel  and  the  rubber  tube,  shown  in  Fig.  36, 
not  using  the  cork,  with  a  strong  solution  of  potassium 
hydrate.  This  liquid  will  absorb  carbon  dioxide,  but  not 


CHEMISTRY    OF    THE    ATMOSPHERE.  83 

carbon  monoxide.  Then  slip  the  end  of  the  rubber  over 
the  end  of  the  long  glass  tube  which  passes  into  the  test- 
tube  in  which  you  caught  the  gas.  Put  a  solid  stopper  in 
place  of  the  short  glass  tube,  and  then  go  on  with  the  work 
as  in  Ex.  49.  When  you  come  to  measure  the  volumes  do 
not  forget  that  you  have  used  the  long  glass  tube  in  the 
test-tube  full  of  gas. 

5.  Finally,  write  a  brief  account  of  your  investigation 
and  its  results. 

2.   Study  the  action  of  phosphorous  on  air. 

We  have  seen  that  phosphorus  burns  in  air  when  it  is 
heated  (Ex.  44);  but  how  will  the  two  behave  if  no  heat 
is  used  ?  Remember  to  handle  phosphorus  with  great  care. 
See  p.  67. 

1.  Place  a  small  piece  of  phosphorus  on  the  end  of  a 
small  wire,  and  put  it   into   a  bottle.     Then    invert   the 
bottle  and  leave  it  standing,  mouth  downward,  in  a  vessel 
of  water  several  hours.     Notice  any  evidence  of  chemical 
change  or  of  absorption,  or  of  any  other  action  which  may 
occur. 

2.  Remove  the  bottle  from  the  water  without  losing  any 
part  of  what  is  in  it,  and  at  once  test  the  gas  which  is  left. 
Decide  what  this  gas  is,  and  then  what  the  phosphorus 
must  have  done. 

3.  See  if  you  can  find  out,  by  measuring,  what  fraction 
of  the  air  the  phosphorus  took  out. 

4.  Write  a  brief  account  of  your  work  and  results. 


COMPOUNDS    OF    NITROGEN,    HYDROGEN, 
AND    OXYGEN. 

WE  have  seen  that  about  four-fifths  of  the  air  is  nitrogen 
gas,  and  that  its  effect  is  simply  to  dilute  the  oxygen  so 
that  combustion  will  be  less  furious  than  it  would  be  in 
oxygen  alone,  and  so  that  the  air  may  be  mild  enough  for 
animals  to  breathe.  Nitrogen  is  just  fitted  to  do  this, 
because  it  has  so  little  affinity  for  other  elements. 

But  nitrogen  can  be  made  to  combine  with  other  ele- 
ments, and  in  fact  there  are  a  great  many  of  its  compounds 
known.  Many  of  these  are  strangely  unlike  the  element 
itself,  for  while  it  is  the  mildest  of  all  things,  these  com- 
pounds are  among  the  most  pungent  and  corrosive  sub- 
stances  to  be  found. 

AMMONIA. 

Ammonia  is  the  compound  of  nitrogen  and  hydrogen. 

Produced  in  two  Ways.  —  There  are  two  ways  in  which 
these  two  elements  can  be  made  to  combine:  one  is  by 
electricity.  If  we  mix  the  gase^,  and  then  send  a  silent 
electric  charge  through  the  mixture  for  a  long  time,  we 
find  some  ammonia  in  the  tube. 

Ammonia  in  small  quantities  is  found  in  the  air,  and  it 
is  likely  that  the  electricity  of  the  atmosphere  has  pro- 
duced it  there. 

The  other  way  to  make  nitrogen  and  hydrogen  combine 
is  to  bring  them  together  just  at  the  moment  when  they 
are  set  free  from  some  other  compounds.  For  example, 
they  are  both  found  in  animal  bodies,  such  as  horns,  hoofs, 
and  flesh.  Now,  when  these  decay,  the  nitrogen  and  hydro- 
gen are  set  free,  but  they  are  together  at  the  same  moment, 

84 


NITROGEN,  HYDROGEN,  AND   OXYGEN.  85 

and  combine  with  one  another.  Neither  escapes  alone,  but 
they  go  off  together  as  ammonia.  Ammonia  may  be  found 
in  the  air  of  stables,  of  farm-yards,  and  of  other  places 
where  animal  matters  are  decomposing. 

THE  NASCENT  STATE.  —  These  gases  are  not  the  only 
things  which  combine  most  readily  just  at  the  moment 
when  they  are  set  free  from  something  else.  Other  ele- 
ments also  seem  to  be  more  active  at  that  moment  than 
at  other  times.  They  are  then  said  to  be  in  the  nascent 
state. 

FORMED  IN  GAS-WORKS.  —  Gas  for  lighting  towns  and 
cities  is  made  by  heating  soft-coal  to  a  cherry-red  heat. 
Among  the  gases  and  vapors  driven  off  are  ammonia  and 
some  of  its  compounds.  These  are  bad  impurities,  and  in 
the  manufacture  of  gas  they  are  washed  out  by  cold  water. 
The  ammonia,  in  this  "ammonia  water"  of  the  gas-house, 
is  saved  by  making  it  combine  with  hydrochloric  acid, 
which  changes  it  to  ammonium  chloride,  or  with  sulphuric 
acid,  which  changes  it  to  ammoniu7n  sulphate.  This  is  the 
source  of  nearly  all  the  ammonia  and  its  compounds,  great 
quantities  of  which  are  used  annually. 

Preparation   of  Ammonia Ammonia  itself  is  made 

by  decomposing   one  of   these   com- 
pounds by  heating  it  with  lime. 

Ex.  53.  —  I  powder  a  very  little 
ammonium  chloride  and  also  a  little 
good  quick-lime.  I  then  mix  them 
well,  and  put  into  a  clean  and  dry 
test-tube  enough  to  half  fill  the 
rounded  bottom.  I  fill  the  mortar 
with  water  colored  blue  by  litmus, 
and  add  only  a  drop  of  hydrochloric  Fig-  *1- 

acid  to  redden  it :  let  this  stand  ready  for  use  when  needed. 
I  take  the  tube  between  my  fingers,  with  my  thumb  over 


86  NITROGEN,  HYDROGEN,  AND   OYYGEN. 

its  mouth,  leaving  a  small  opening  at  the  lower  edge,  and 
hold  it  some  time  in  the  hot  air  above  the  flame,  a  little 
inclined,  as  shown  in  Fig.  41.  Note 

The  deposits  of  moisture  on  the  cold  parts  of  the  tube. 

The  odor  at  the  mouth  of  the  tube. 

This  is  the  odor  of  ammonia. 

What  two  substances  seem  to  have  been  produced  ? 

By  this  time  the  decomposition  of  the  mixture  is  at  an 
end,  and  I  bring  the  mouth  of  the  tube  down  into  the  red- 
dened litmus-water,  still  holding  the  tube 
so  much  inclined  (Fig.  42)  that  the  white 
solid  will  not  fall  down   into  the  water. 
As  the  tube  cools  the  red  water  rises  in  it. 
But  it  will  rise  much  further  than  it  would 
if  the  tube  were  heated  without  the  mix- 
ture.    (Try  an  empty  tube  in  the  same  way,  and  see  how 
far  the  water  will  rise.) 

What  property  of  the  gas  does  this  show  ? 
Note  the  change  of  color  in  the  water. 
Compare  this  change  with  that  in  Ex.  48. 

THE  FACTS.  —  We  find  that  by  heating  the  ammonium 
chloride  with  lime  we  get  water,  condensing  in  droplets  on 
the  tube;  ammonia,  which  we  know  by  its  familiar  pun- 
gent odor ;  and  a  white  solid  left  clinging  to  the  bottom  of 
the  tube,  which  is  calcium  chloride. 

We  see,  too,  that  ammonia  is  a  gas,  but  a  gas  which  is 
soluble  in  water.  Now  the  so-called  ammonia  in  commerce 
is  a  liquid.  It  is,  clearly,  not  the  real  ammonia.  The  fact 
is,  it  is  water  with  as  much  as  it  will  hold  of  the  ammonia 
gas  in  solution. 

One  cubic  centimeter  of  water  at  15°  C.  will  hold  783  cc. 
of  this  gas,  and,  like  all  other  gases,  ammonia  is  more  sol- 
uble in  colder  water.  At  0°  C.  the  cubic  centimeter  of 


NITROGEN,   HYDROGEN,  AND   OXYGEN.  87 

water  will  absorb  1148  cc.  of  this  gas.     This  strong  solu- 
tion of  ammonia  is  known  as  ammonium  hydrate. 

By  warming  this  liquid  ammonia,  the  gas  itself  can  be 
obtained  in  great  abundance. 

Ex.  54'  —  To  do  this  I  arrange  the  apparatus  as  in  Fig. 
43.  I  put  10  cc.  or  15  cc.  of  the  liquid  ammonia  in  the 
side-neck  flask,  close  its  mouth 
and  connect  it  with  the  short 
tube  of  a,  whose  long  tube  is 
joined  to  the  short  one  of  b. 
The  stoppers  must  close  the 
flasks  air-tight. 

I  put  the  short  tube  of  a  next 
the  flask,  because  this  gas  is 
lighter  than  air.  It  will  collect 
in  the  upper  part  of  a,  and 
push  the  air  out  through  the 
long  tube  into  the  upper  part  r1*-*3- 

of  6,  and  afterwards  out  of  the  long  tube  of  b,  until  both 
flasks  are  full. 

I  now  make  the  lamp-flame  very  small,  so  that  only  a 
current  of  hot  air  will  warm  the  liquid  in  the  flask.  The 
gas  will  soon  escape  freely.  Some  water-vapor  goes  over 
with  it,  but  1  use  as  gentle  heat  as  I  can  to  keep  it  bub- 
bling ;  the  water  does  not  boil ;  the  bubbles  are  ammonia 
gas,  mixed  with  little  vapor. 

Note  the  odor  of  the  gas  which  escapes  from  the  open 
tube  of  b;  it  will  be  more  and  more  pungent  until  the  air 
is  all  out  of  the  flask. 

Ex.  55.  —  Moisten  a  stick  with  hydrochloric  acid  and 
hold  it  just  above  the  tube  of  b. 

What  evidence  of  chemical  action  do  you  find  ? 
Compare  this  with  Ex.  9. 


88  NITROGEN,  HYDROGEN,  AND   OXYGEN. 

Ex.  56.  —  I  take  both  rubber  tubes  from  a,  and  at  once 
plunge  the  stoppered  mouth  of  the  flask  down  into  a  vessel 
of  water  (Fig.  44). 
What  is  the  result  ? 
What  does  it  teach  about  ammonia 
gas? 

Ex.  57.  —  I  redden  some  blue  lit- 
Fi«-  **•  mus  with  as  little  hydrochloric  acid 

as  will  do  it,  and  then  pour  into  it  some  of  the  water  which 
has  just  now  dissolved  the  gas  in  a. 

How  does  the  ammonia  show  its  presence  in  the  water  ? 

Has  this  ammonia-water  any  taste  or  odor? 

THE  FACTS.  —  Dry  ammonia-gas  is  invisible  and  much 
lighter  than  air.  Its  solution  in  water  has  a  caustic  taste, 
and  will  bring  back  the  blue  color  of  litmus  which  has  been 
reddened  by  acid. 

Ammonia  is  a  stimulating  gas  to  breathe :  on  this  ac- 
count it  is  used  to  revive  the  faint,  and  sometimes  to 
overcome  the  effects  of  an  anaesthetic,  like  ether  or  chlo- 
roform. 

Ammonia  and  hydrochloric  acid  combine  at  once,  when- 
ever brought  together,  and  form  ammonium  chloride.  The 
white  cloud  in  Ex.  55  was  a  cloud  of  ammonium  chloride. 

Ammonium  Salts.  —  Ammonia  acts  also  on  other  acids, 
and  so  forms  a  large  number  of  compounds,  which  as  a 
class  are  called  ammonium  salts. 

Ex.  58.  —  I  put  10  cc.  of  water  into  a  small  wide-mouth 
bottle  and  add  2  cc.  strong  sulphuric  acid.  I  place  this  in 
a  porcelain  dish  and  drop  into  it  a  small  clipping  of  blue 
litmus-paper.1  I  now  add  strong  ammonia  water  (ammo- 
nium hydrate)  little  by  little,  shaking  the  mixture  well 

1  Filter-paper  soaked  in  a  strong  solution  of  litmus  and  afterward 
dried. 


NITROGEN,  HYDROGEN,  AND   OXYGEN. 


89 


each  time,  until  the  red  paper  turns  blue.  If  now  I  add 
drop  by  drop  of  the  dilute  acid,  I  can  reach  the  point 
when  the  paper  is  just  reddened  by  the  last  drop,  and 
when  another  drop  of  ammonia  will  make  it  blue  again.  I 
do  this.  And  then  I  put  the  dish  over  a  small  flame  and 
evaporate  (Fig.  10)  the  liquid,  until  a  white  rim  is  seen 
around  its  edge  on  the  dish,  and  then  let  it  cool. 

While  waiting  for  the  liquid  to  evaporate  I  begin  the 
next  experiment. 

Ex.  59.  —  I  mix  5  cc.  of  water  and  5  cc.  strong  nitric 
acid,  add  the  blue  litmus-paper  and  then  the  ammonium 
hydrate,  until  the  last  drop  turns  the  paper  blue.  I  then 
evaporate  this  liquid  to  about  one-fourth  its  bulk,  and  let 
it  cool. 

If  the  liquids  were  evaporated  enough,  crystals  of  a  white 
solid  will  be  seen  in  each  when  it  is  cold,  or  the  whole  may 
become  a  solid  white  mass. 

Ex  60.  —  I  take  a  little  of  one  of  these  white  solids  to 
test  its  action  on  litmus.  I  first  pour  upon  it,  and  then 
quickly  off  again,  a  little  water  —  just  to  wash  it.  And 
then  I  add  water  to  dissolve  it.  I  take  two  clippings 
of  blue  litmus-paper,  moisten  one  with  water,  and  then 
redden  it  by  holding  it  in  the  mouth  of  the  bottle  of 
hydrochloric  acid,  and  then  put  both  into  the  solution. 
No  change  of  color  should  occur  in  either. 

These  white  solids,  made  by  the  action  of  ammonia  on 
sulphuric  and  nitric  acids,  are  examples  of  ammonium 
salts. 

But  why  did  we  use  the  litmus  ?  Simply  to  show 
when  the  chemical  change  was  ended.  We  have  found 
that  blue  litmus  is  reddened  by  an  acid  in  every  case,  and 
that  ammonia  will  bring  back  the  blue  color.  But  when 
there  is  just  enough  ammonia  to  use  up  all  the  acid, 


90  NITROGEN,   HYDROGEN,  AND 

neither  the  blue  nor  the  red  is  changed.  The  ammonia 
and  the  acid  neutralize  each  other,  and  the  litmus  shows 
the  end  of  this  action. 

Do  not  leave  this  until  you  see  clearly  why  the  two  neu- 
tralize each  other.  Consult  p.  57  for  the  law. 

Composition  of  Ammonia  by  Volume.  —  It  is  found 
by  analysis  that  ammonia  always  yields  just  three  times 
as  many  cubic  centimeters  of  hydrogen  as  of  nitrogen. 
Its  composition  by  volume  is : 

3  measures  hydrogen  to  1  measure  nitrogen. 

But  another  question  is,  How  much  ammonia  gas  would 
these  3  of  hydrogen  and  1  of  nitrogen  make  ?  It  has  been 
found  by  analysis  that  20  cc.  of  ammonia  will  give  30  cc. 
of  hydrogen  and  10  cc.  of  nitrogen.  That  is  to  say,  30  cc. 
of  hydrogen  and  10  cc.  of  nitrogen  make  20  cc.  of  am- 
monia. 

Three  measures  of  hydrogen  and  one  measure  of  nitro- 
gen make  two  measures  of  ammonia.  Or  four  volumes  of 
the  constituents  are  condensed  to  two  volumes  of  the 
compound. 

Compare  this  curious  fact  with  another  noted  under  the 
composition  of  water,  p.  56. 

NITRIC    ACID. 

Nitric  acid  is  a  compound  of  nitrogen,  hydrogen,  and 
oxygen.  It  is  one  of  the  strongest  of  acids,  and  one  of 
the  most  useful. 

Occurs  in  Combination. — Very  small  quantities  of 
this  acid  exist,  free,  in  the  air:  it  is  in  its  compounds  that 
it  is  mostly  found.  Two  of  these  compounds  occur  in  large 
quantities  in  some  parts  of  the  earth  :  they  are  "  saltpetre," 
whose  true  name  is  potassium  nitrate,  and  "  Chilian  salt- 
petre," or  sodium  nitrate. 


NITROGEN,   HYDROGEN,  AND   OXYGEN.  91 

Made  from  Sodium  Nitrate.  —  To  get  the  nitric  acid 
the  sodium  nitrate  is  heated  with  sulphuric  acid.  Sulphu- 
ric acid  is  still  stronger  than  nitric  acid,  and  will  drive  the 
latter  out  of  the  nitrate  in  order  to  take  its  place.  The 
nitric  acid  is  driven  out  in  the  form  of  vapor,  but  it  is 
carried  into  a  cold  vessel,  where  the  vapor  is  condensed 
to  a  liquid. 

Properties.  —  Nitric  acid  when  pure  has  no  color,  but 
it  is  intensely  sour  and  very  corrosive.  It  will  redden 
litmus  like  other  acids,  but  will  not  stop  with  this :  it  will 
go  right  on  to  destroy  the  red  color.  Try  this  by  putting 
a  piece  of  litmus-paper  into  a  little  of  the  strong  acid. 
It  will  first  turn  red,  soon  afterward  yellow,  and  in  a  little 
time  the  paper  will  easily  break  to  pieces.  In  the  same 
way  it  will  form  yellow  stains  upon  the  fingers,  and  upon 
the  garments,  and,  in  fact,  upon  all  organic  bodies.  The 
acid  may  be  washed  away  by  water,  or  it  may  be  neutral- 
ized by  ammonia,  but  the  yellow  color  will  remain. 

Ex.  61.  —  Wet  some  pieces  of  woolen  cloth  with  drops 
of  nitric  acid,  with  drops  of  hydrochloric  acid,  and  of 
sulphuric  acid.  Wait  until  the  color  is  changed  by  all, 
and  then  try  the  effect  of  ammonia  on  them.  Note  the 
difference. 

The  strong  nitric  acid  in  commerce  is  by  no  means  pure : 
in  fact,  it  is  almost  half  water,  and  there  are  several  other 
impurities  besides  water,  in  small  quantities.  By  distil- 
ling a  mixture  of  this  acid  with  strong  sulphuric  acid  the 
pure  and  concentrated  nitric  acid  is  obtained. 

Decomposition  of  Nitric  Acid.  —  This  acid  is  very 
easily  decomposed.  It  is  decomposed  by  light.  When 
standing  in  the  sunlight,  the  upper  part  of  the  bottle  of 
acid  will,  after  a  time,  be  seen  full  of  a  reddish  vapor; 
this  is  set  free  from  the  acid  by  light,  and  water  is 
formed  at  the  same  time.  The  yellow  color  of  the  com- 


92  NITROGEN,   HYDROGEN,  AND   OXYGEN. 

mon  acid  is  due  to  this  reddish  vapor,  some  of  which 
is  dissolved  in  the  liquid. 

THE  NITRATES. — Nitric  acid  is  easily  decomposed  by 
almost  any  metal.  One  can  see  this  action  by  putting 
small  bits  of  copper  or  lead  in  a  test-tube  and  covering 
them  with  dilute  nitric  acid.  But  the  fumes  are  very  nox- 
ious, and  the  experiment  should  be  made  on  a  small  scale, 
or  else  in  the  open  air.  The  same  red  vapor,  seen  when 
the  acid  is  decomposed  by  light,  is  set  free  in  abundance 
by  the  metal.  Water  is  also  formed,  and  beside  these  a 
salt  of  nitric  acid  is  produced.  These  salts  of  nitric  acid 
are  called  nitrates.  The  salt  made  with  copper  is  blue,  and 
it  is  called  copper  nitrate ;  that  made  with  lead  is  white, 
and  is  called  lead  nitrate. 

This  decomposition  of  nitric  acid  by  a  metal  will  be 
better  understood  further  on,  when  we  study  Ex.  62. 

These  nitrates  are  all  soluble  in  water,  and  so  when  a 
metal  is  changed  into  a  nitrate  the  metal  seems  to  dis- 
solve, but  it  is  always  the  nitrate  which  is  in  solution,  and 
not  the  metal. 

AQUA  REGIA. — Nearly  all  the  metals  are  thus  changed 
into  nitrates  by  nitric  acid;  but  gold  and  platinum  are  the 
exceptions.  To  dissolve  these  metals  we  need  a  mixture 
of  nitric  and  hydrochloric  acids.  Neither  of  these  alone 
can  attack  gold  or  platinum,  but  the  two  together  will 
dissolve  them  readily.  The  mixture  of  these  two  acids 
is  called  aqua  regia.  But,  as  we  shall  see,  the  metals 
dissolved  in  aqua  regia  are  not  changed  into  nitrates,  but 
into  compounds  of  chlorine,  called  chlorides. 

NITROGEN    OXIDES. 

Investigate   the   Decomposition  of    Nitric   Acid 

We  have  just  seen  that  when  nitric  acid  is  decomposed 
reddish  vapors  are  set  free.  What  are  these  vapors  ? 


NITROGEN,  HYDROGEN,  AND   OXYGEN.  gj 

Let  us  study  the  action  by  experiment.  We  will  decom- 
pose the  acid  by  copper. 

Ex.  62.  —  I  fit  up  my  apparatus  for  making  and  collect- 
ing gases  as  usual  for  a 
gas  heavier  than  air  (Fig. 
45),  the  long  tubes  of  the 
flasks  a,  b,  c  toward  the 
side-neck  flask.  Into  both 
a  and  b  I  put  water,  which 
the  cut  shows  only  in 
a,  but  none  in  c.  After 
the  connections  are  made, 
I  put  about  seven  grams 
of  small  pieces  of  copper-  :fjj 
foil,  or  thin  sheet-copper,  Fig- 45> 

in  the  side-neck  flask,  pour  in  about  25  cc.  of  dilute  nitric 
acid,  half  water,  and  close  the  flask  with  its  air-tight  stop- 
per. The  chemical  action  sets  in  at  once.  No  heat  is 
needed  to  start  it. 

Note  the  change  in  the  color  of  the  acid. 

Trace  the  changes  of  color  as  they  occur  in  s,  a,  b}  c. 

We  see  that  a  red  gas  quickly  fills  the  flask  s,  and  goes 
over  into  a,  b,  c,  but  that  the  red  color  disappears  from 
s,  a,  and  b,  and  stays  in  c  for  a  much  longer  time. 

How  many  kinds  of  gas  are  evidently  in  the  flasks  ? 

When  a  and  b  are  clear,  and  c  still  full  of  red-brown  gas, 
I  disjoin  the  rubber  tube  of  c,  remove  the  stopper  carefully, 
pour  in  gently  a  few  cubic  centimeters  of  water,  and  return 
the  stopper  to  its  place  as  tightly  fitted  as  before.  I  now 
close  the  ends  of  both  glass  tubes  with  my  finger,  which  1 
can  easily  do  if  they  are  at  the  same  level,  lift  the  flask 
and  shake  it  well.  Note  the  disappearance  of  the  red  gas. 
I  next  plunge  the  finger  and  tubes  under  water,  and  take 
the  finger  away.  Note  the  inrush  of  water. 


94  NITROGEN,   HYDROGEN,  AND   OXYGEN. 

Why  did  the  color  of  the  gas  disappear  with  water  ? 
Why  did  the  water  rush  in  when  the  tubes  were  opened  ? 
What  property  of  the  red  gas  is  thus  discovered? 
Ex.  63.  —  I  now  disjoin  the  rubber  tubes  of  I,  and  then 
invert  the  flask  and  let  the  water  run  out  of  the  short  tube. 
Of  course  air  will  run  in  through  the  long  tube  and  mix 
with  the  colorless  gas  within.     The  red  gas  is  reproduced ! 
This  is  an  important  discovery.     If  air  will  change  the 
colorless  gas  into  the  red  gas,  perhaps  it  was  in  this  way 
that  the  red  gas  was  made  in  the  flasks  at  first,  for  they 
were  full  of  air  when  the  action  began  in  s.     If  I  could 
keep  the  air  away,  while  the  copper  and  nitric  acid  act  on 
each  other,  would  the  red  gas  appear  at  all? 

Now  I  can  keep  the  air  away,  and  answer  this  question, 
by  putting  carbon  dioxide  into  tlie  flasks  in  place  of  the  air. 
Ex.  64-  —  I  disjoin  the  rubber  tubes  of  a,  and  empty  the 
contents  of  *  into  a  porcelain  dish  to  be  examined  after- 
ward.    I  then  join  the  side-neck 
with  the  long  tube   of  another 
flask   (Fig.  46).      I  put  20  cc. 
dilute   nitric   acid,   half    water, 
into  s,   drop  in  gently  two   or 
three  pieces  of  marble  as  large 
as  peas,  and  close  the  flask.    Car- 
bon   dioxide   will   be    set   free, 
drive  the   air   before  it   out   at 
the  open  short  tube,  and  will 
P>  soon  fill  the  flask.     I  then  open 
Tis-  *6-  s,  drop  in  some  bits   of  copper, 

and  quickly  close  it  again.  The  nitric  acid  and  copper  now 
act  in  the  absence  of  air.  Do  they  yield  the  red  gas  ? 
None  will  be  seen  if  the  air  was  all  expelled.  Do  they 
yield  the  same  colorless  gas  as  before  ?  I  mix  air  with  the 
gas  in  c  ;  the  red  gas  instantly  appears,  as  it  did  in  Ex.  63. 


NITFJGEN,   HYDROGEN,  AND   OXYGEN. 


95 


Our  experiments  clearly  prove  that  when  copper  decom- 
poses nitric  acid,  only  •  a  colorless  gas  is  set  free.  But 
when  this  colorless  gas  meets  with  air,  another,  a  red- 
brown  gas,  is  formed.  At  the  same  time  a  blue  compound 
^s  made  which  stays  in  the  liquid.  The  colorless  gas  is  a 
compound  of  nitrogen  and  oxygen,  called  nitric  oxide,  and 
the  red-brown  gas  is  another  compound  of  nitrogen  and 
oxygen,  called  nitroyen  peroxide.  The  blue  compound  is 
copper  nitrate.  It  may  be  obtained  in  blue  crystals  by  fil- 
tering the  liquid  and  evaporating  it  until,  on  cooling,  the 
crystals  form.  (Try  it.) 

When  nitric  oxide  mixes  with  air  it  instantly  combines 
with  oxygen  and  becomes  nitrogen  peroxide. 

Nitrous  Oxide.  —  There  is  another  compound  of  nitro- 
gen and  oxygen  called  nitrous  oxide.  It  is  not  usually 
made  by  the  decomposition  of  nitric  acid  directly,  but  by 
decomposition  of  ammonium  nitrate,  and  this  is  done  by 
means  of  a  gentle  heat,  which  breaks  the  nitrate  into  water 
and  nitrous  oxide.  Thus  : 

Ex.  65.  —  I  put  from  7  to  10  grams  of  ammonium  nitrate 
into  the  side-neck 
flask,  which  should 
be  dry,  and  join  the 
flasks  «,  b,  c,  as  usual 
for  a  heavy  gas.  To 
condense  the  steam, 
I  put  the  empty  flask 
a  into  a  dish  of  cold 
water,  —  ice-water  is 
best.  It  may  be  held 
down  in  the  water  by 
a  cord  passing  over  Fig-  47- 

the  stopper  and  around  under  the  heavy  dish  of  water.     To 
decompose  the  nitrate  1  use   the   gentle   heat  of  a  small 


96  NITROGEN,  HYDROGEN,  A  XI)    OXYGEN. 

flame,  just  hot  enough  to  melt  and  keep  it  gently  boiling. 
The  nitrate  slowly  wastes  away,  and  when  but  about  one- 
fifth  remains  I  withdraw  the  lamp. 

Flasks  s  and  a  prove  that  water  is  produced.     How  ? 

Test  the  gas  in  b  with  the  flame  of  a  splinter  of  wood. 

Note  the  color,  and  the  odor,  of  the  gas  in  c. 

THE  FACTS.  —  AmmQn^njn_:Jiiteate  contains  nitrogen,  hy- 
drogen, and  oxygen,  and  when  it  is  decomposed  the  nitro- 
gen and  hydrogen  separate,  each  taking  a  part  of  the 
oxygen  with  it.  The  nitrogen  and  oxygen  form  the  nitrous 
oxide,  while  the  hydrogen  and  oxygen  form  water.  The 
water  is  condensed  in  a  (Fig.  47),  while  the  nitrous  oxide 
is  collected  in  a,  b,  and  c. 

Nitrous  oxide  is  a  colorless  gas  in  which  bodies  will  burn 
with  almost  the  same  vigor  as  in  oxygen  itself.  But  its 
most  remarkable  action  is  upon  a  person  who  breathes  it. 
Breathed  in  small  quantities  it  intoxicates,  and  often  causes 
a  disposition  to  laughter.  On  this  account  it  is  commonly 
known  as  laughing-gas.  But  if  its  use  be  continued  a  few 
minutes,  it  will  produce  complete  insensibility,  and  if  con- 
tinued, death.  It  is  much  used  to  render  patients  insensi- 
ble to  pain  in  minor  surgical  operations,  such  as  the  extrac- 
tion of  teeth.  The  insensibility  lasts  a  few  minutes  only ; 
it  is  quickly  banished  by  fresh  air. 

The  Five  Nitrogen  Oxides.  —  There  are  two  other 
compounds  of  nitrogen,  making  in  all  five.  Here  are  five 
entirely  different  kinds  of  substance  made  out  of  the 
same  two  elements.  But  how  can  the  same  elements  make 
different  compounds  ?  By  combining  in  different  propor- 
tions. When  the  colorless  nitric  oxide  touches  the  air  it 
takes  in  more  oxygen  and  becomes  the  red  nitrogen  per- 
oxide. Different  weights  of  these  elements  unite. 

Let  N  stand  for  nitrogen  and  0  for  oxygen.  By  analy- 
sis it  has  been  found  that 


NITROGEN,  HYDROGEN,  AND    OXYGEN.  97 

Nitrous  oxide  contains  28  of  N  and  16  of  O 
Nitric  oxide  «  14  «  "  "  16  "  « 

Nitrous  anhydride  «  28  «  "  «  48  «  « 
Nitrogen  peroxide  "  14  «  "  "  32  "  " 
Nitric  anhydride  "  28  "  "  "  80  "  " 

The  properties  of  a  compound  depend  on  the  relative 
weights  of  the  elements  in  it.  This  fact  is  clearly  shown 
by  these  nitrogen  oxides. 

The  Law  of  Multiple  Proportions It  is  a  curious 

fact  that  the  relative  quantities  of  oxygen  in  this  table  of 
nitrogen  oxides  are  all  either  16,  or  else  2  or  3  or  5  times 
16.  So,  too,  in  the  case  of  the  nitrogen  the  quantities  are 
either  14,  or  twice  14.  In  both  cases  alike,  the  larger 
numbers  are  all  exact  multiples  of  the  smallest.  Now 
chemists  have  found  this  to  be  true  in  a  great  many  other 
cases  where  two  elements  make  more  than  one  compound. 
In  fact  they  have  met  no  exception.  This  causes  them  to 
feel  quite  sure  that  all  elements  are  alike  in  this  respect, 
and  they  state  this  conclusion  as  follows : 

If  one  element  combines  with  another  in  more  than  one 
proportion,  these  proportions  are  all  exact  multiples  of  some 
one  fixed  number. 

And  this  important  statement  of  fact  is  known  as  the 
"law  of  multiple  proportions."  The  student  should  now 
remember  the  "  law  of  constant  proportions  "  ( p.  57),  for 
these  two  laws  together  cover  the  most  vital  facts  about 
the  combination  of  elements. 

Combination  of  Definite  Weights These  two  laws 

show  very  clearly  that  the  elements  never  combine  except 
in  certain  definite  weights. 

The  definite  weights  of  oxygen  and  hydrogen  in  water 
are  in  the  ratio  of  16  to  2.  Sixteen  grams  of  oxygen  and 
two  grams  of  hydrogen  will  unite  without  leaving  any  of 
either.  But  if  we  pass  an  electric  spark  through  a  mixture 


98  NITROGEN,  HYDROGEN,  AND    OXYGEN. 

of  16  g.  of  oxygen  with  3  g.  of  hydrogen,  just  1  g.  of  hydro- 
gen will  be  left. 

The  definite  weights  in  which  oxygen  and  nitrogen 
always  combine  have  the  ratio  of  16  to  14. 

The  definite  weights  of  hydrogen  and  chlorine  which 
make  their  compound,  hydrochloric  acid,  are  as  1  to  35.5. 
In  other  compounds  of  chlorine  the  definite  weight  of 
chlorine  used  may  be  2  or  3  or  some  other  whole  number 
of  times  35.5.  And  in  other  compounds  of  hydrogen  the 
definite  weight  of  hydrogen  may  be  2  or  3  or  some  other 
whole  number  of  times  1. 

Combining  Weights,  —  These  numbers  which  show  the 
ratios  of  the  smallest  definite  proportions  by  weight  in 
which  these  elements  ever  combine  with  anything  else, 
are  called  combining  weights.  Thus  we  say 

The  combining  weight  of  Hydrogen  is     ...  1 

"  "  "       "  Oxygen      "      ...  16 

«  "  «       "  Nitrogen    "      ...  14 

«  "  "        "  Chlorine    "...  35.5 

And  we  mean  that  the  smallest  weight,  of  chlorine  for 
example,  which  we  can  find  in  any  compound  is  just  35.5 
times  as  large  as  the  smallest  weight  of  hydrogen  which 
can  be  found  in  any  of  its  compounds. 

To  find  these  numbers  —  the  combining  weights  —  is  one 
of  the  most  difficult  problems  in  chemistry.  The  student 
is  not  yet  ready  to  see  how  it  is  done.  But  it  has  been 
done  for  the  whole  list  of  elements.  Every  element  has  a 
combining  weight  assigned  to  it. 

EXERCISES. 

1.   Make  some  Nessler's  reagent  as  follows  : 

1.  Make  a  solution  of  potassium  iodide,  say  6  g.  in  20  cc. 
of  distilled  water,  or  of  the  best  spring  water. 


NITROGEN,  HYDROGEN,  AND   OXYGEN.  99 

2.  Make  a  strong  solution  of  mercuric  chloride,  say  6  g. 
in  60  cc.  of  water. 

3.  Add  the  mercuric  chloride  solution,  little  by  little,  to 
the  potassium  iodide,  until  a  small  portion  of  the  precipi- 
tate will  not  disappear  when  shaken  or  stirred. 

4.  Make  a  strong   solution    of   potassium  hydrate,  say 
10  g.  in  15  cc.  of  water,  and  when  cold  add  this  to  the 
mixture  already  made. 

Finally,  let  this  mixture  stand  until  it  is  perfectly  clear. 
The  clear  liquid  is  called  Nessler's  reagent. 
2.  Study  the  effect  of  Nessler's  reagent  on  solutions  contain- 
ing ammonia. 

1.  Add  a  drop  or  two  of  ammonium  hydrate  to  a  test- 
tube  nearly  filled  with  distilled  or  spring  water.     Then  add 
1  cc.  of  the  Nessler's  solution.     Mix  it  well,  and  note  the 
color  of  the  mixture. 

Find  out  whether  less  than  a  drop  of  ammonia  will  yield 
this  color  in  the  same  quantity  of  water.  Or  how  little 
you  can  use  and  still  be  able  to  detect  the  color. 

2.  Put  a  little  solution  of  ammonium  chloride  in  the 
water,  instead  of  ammonia,  and  test  it  with  the  Nessler's 
solution. 

Does  the  ammonia  of  the  ammonium  chloride  yield  the 
same  color  ? 

The  fact  is  that  Nessler's  solution  is  the  most  delicate 
test  for  ammonia,  always  showing  the  presence  of  that  sub- 
stance by  a  yellow  color,  which  has  a  light  straw  tint 
when  very  little  ammonia  is  present,  and  a  deep  orange 
tint  when  there  is  much. 

8.  Learn  by  this  test  whether  rain-water  contains  am- 
monia. 

Why  should  rain-water  contain  ammonia  ? 

4-  Test  the  drinking-water  of  the  neighborhood  for  am- 
monia. 


100  NITROGEN,  HYDROGEN,  AND   OYYGEN. 

3.  Study  the  effect  of  nitric  acid  on  ferrous  sulphate,  some- 
times called  "  copperas.11 

1.  Into  a  little  dilute  nitric  acid  in  a  test-tube  drop  a 
good  crystal  of  the   ferrous  sulphate.     Do  not   shake  it. 
Notice  the  color  which  appears  in  the  liquid  around  the 
crystal. 

2.  See  how  dilute  you  can  make  the  acid  and  still  be 
able  to  detect  this  color  when  a  crystal  of  the  sulphate  is 
used. 

3.  Try  the  solution  of  a  nitrate,  say  potassium  nitrate, 
instead  of  nitric  acid,  in  the  same  way. 

Does  the  color  now  appear  around  the  crystal  ?  If  not, 
there  is  probably  little  or  no  free  nitric  acid  present. 

4.  Mix  a  little  solution  of  the  potassium  nitrate  with  a 
solution  of  the  sulphate,  incline  the  tube,  and  let  a  little 
concentrated  sulphuric  acid  run  down  the  inside  of  the 
glass,  to  the  bottom.     Do  not  shake  it.  * 

The  color  should  now  appear  as  a  ring,  where  the  liquids 
touch  each  other. 

If  so,  then  why  did  it  not  in  the  other  case  ? 

The  fact  is  that  strong  sulphuric  acid  decomposes  the 
nitrate  and  sets  its  nitric  acid  free.  And  then  the  free 
nitric  acid  shows  itself  by  the  color  it  makes  by  acting  on 
the  crystal. 

5.  Make  the  experiment  again  with  potassium   nitrate 
and  sulphuric  acid,  but  add  the   ferrous  sulphate  to  the 
liquid  when  hot. 

Ferrous  sulphate  is  a  delicate  and  much-used  test  for 
nitric  acid  and  the  nitrates.  It  must  be  used  in  cold  solu- 
tions :  the  brown  color  disappears  on  heating. 

6.  Get  a  little  of  some  white  solid,  the  name  of  which 
you  do  not  know,  from  the  teacher,  or  a  friend  who  knows 
what  it  is,  and  see  if  you  can  tell  by  the  copperas  test 
whether  it  is  a  nitrate  or  not. 


THE    COMPOSITION    OF    PLANTS. 

THE  substances  which  exist  in  plants,  or  which  may  be 
made  from  them,  are  so  many  that  we  cannot  undertake 
to  study  them  all.  The  most  that  we  can  do  now  is  to 
ascertain  the  elements  of  which  plants  are  made,  and  per- 
haps a  few  of  their  simpler  compounds. 

Let  us  examine  a  piece  of  wood  as  follows  : 

Ex.  66.  —  I  take  a  splinter  of  well-dried  pine  wood, 
about  as  large  and  long  as  a  common  match,  drop  it  into  a 
test-tube,  and  then  heat  it  slowly  by  holding  the  tube 
almost  horizontally  just  above  the  tip  of  the  lamp-flame, 
and  move  the  tube  back  and  forth  to  heat  the  length  of  the 
wood. 

Notice  the  dew  on  the  cold  walls ;  what  does  this  show  ? 

Notice  the  vapors ;  do  they  condense  or  go  off  as  gases  ? 

Notice  whether  any  other  liquid  than  water  is  formed. 

Describe  the  stick  after  the  changes  are  over. 

The  Pacts.  —  When  Avood  is  heated  in  a  close  vessel, 
where  there  is  not  air  enough  to  burn  it,  there  are  many 
new  products  of  its  decomposition.  Some  are  gaseous ; 
these  escape  into  the  air.  Some  are  liquid;  these  con- 
dense on  the  cold  parts  of  the  vessel.  A  black  solid  is 
left  which  no  heat  seems  to  affect.  Among  the  liquid 
products  is  water,  —  the  dew  seen  on  the  walls  of  our 
tube;  and  the  black  solid  which  was  left  behind  is  char- 
coal, which  is  the  element  carbon,  almost  pure.  But  water 
is  always  made  up  of  hydrogen  and  oxygen,  and  as  water 
comes  from  the  well-dried  wood,  the  wood  must  contain 
these  elements  also.  Thus  we  prove  that  wood  contains 
carbon,  hydrogen,  and  oxygen. 

101 


102  COMPOSITION    OF  PLANTS. 

By  extending  our  experiments  to  other  kinds  of  vege- 
table matter  we  find  in  them  the  same  elements :  carbon, 
hydrogen,  and  oxygen.  Every  blade  of  grass,  every  leaf 
and  flower,  and  every  kind  of  seed  and  fruit,  contain  these 
three  elements,  and  they  contain  very  little  of  any  others. 

Plants  do  indeed  contain  other  elements  than  these. 
Nitrogen  is  found  in  them ;  in  small  quantities  to  be  sure, 
but  it  must  not  be  overlooked,  because  it  is  one  of  the  most 
important  elements  in  the  vegetable  food  of  animals. 

Besides  nitrogen  there  are  several  other  elements  in 
minute  quantities,  which,  with  carbon,  hydrogen,  and  oxy- 
gen, enter  into  the  composition  of  plants. 

When  wood  or  any  other  vegetable  matter  is  burned, 
these  four  elements  disappear,  and  nothing  but  a  little 
ash  remains ;  but  this  ash  contains  all  the  other  elements 
of  the  substance.  How  small  the  quantity !  It  seldom 
amounts  to  one  tenth  of  the  whole.  In  every  100  pounds 
of  vegetable  matter,  from  90  to  97  pounds  are  made  up  of 
carbon,  hydrogen,  oxygen,  and  nitrogen.  All  these  facts 
have  been  established  by  experiments. 

The  Food  of  Plants An  animal,  to  live  and  grow, 

must  be  supplied  with  food.  The  same  is  true  of  plants : 
they  must  be  supplied  with  nourishment  which  contains 
all  the  elements  they  need  to  promote  their  growth.  Now 
carbon,  hydrogen,  and  oxygen,  with  a  little  nitrogen,  and 
very  small  quantities  of  a  few  other  elements,  make  up 
every  part  of  any  plant.  These  the  plant  must  get  in 
some  way,  else  it  cannot  flourish.  If  any  of  them  are 
lacking,  the  plant  suffers  even  if  it  does  not  die.  The 
food  of  plants  must  contain  all  these  elements. 

The  plant  gets  its  carbon  from  carbon  dioxide.  It  gets 
its  hydrogen  and  oxygen  from  water.  It  gets  its  nitrogen 
from  ammonia,  and  as  nine-tenths  of  the  weight  of 
plants  is  made  up  of  carbon,  hydrogen,  oxygen,  and  nitro- 


COMPOSITION    OF   PLANTS.  103 

gen,  it  is  easy  to  see  that  the  three  substances  just  named 
must  be  the  food  upon  which  plants  must  chiefly  live. 

BUT  HOW  CAN  A  PLANT  TAKE  FOOD?  —  Every  plant  has 
a  multitude  of  mouths.  There  is  one  at  the  end  of  every 
little  rootlet  in  the  soil,  and  there  are  a  host  of  them 
on  the  under  side  of  every  leaf.  Each  little  root-mouth 
of  a  growing  plant  is  taking  in  liquid  food  from  the  soil, 
and  each  little  leaf-mouth  is  at  the  same  time  taking 
gaseous  food  from  the  air. 

The  liquid  which  enters  the  roots  of  a  plant  is  water 
in  which  many  substances  of  the  soil  are  dissolved.  It 
contains  compounds  of  ammonia,  from  which  the  plant  can 
get  nitrogen,  and  it  also  furnishes  the  plant  with  those 
other  elements  which  it  needs  in  small  quantities,  those 
which  make  up  the  ash  which  is  left  when  the  plant 
is  burned. 

The  gaseous  food  which  enters  the  leaves  of  a  plant 
is  the  carbon  dioxide  and  water-vapor  of  the  air.  From 
these  gases  the  plant  gets  carbon,  hydrogen,  and  oxygen,  — 
the  three  most  abundant  elements  needed  in  its  growth. 

The  food  of  plants  must  be  decomposed  before  its  carbon, 
hydrogen,  oxygen,  and  other  elements  can  nourish  them. 
These  elements  then  combine  again  in  very  different  ways 
to  produce  all  the  materials  of  which  the  parts  of  a  plant 
are  made,  such  as  starch,  sugar,  wood-fiber,  gums,  oils,  and 
coloring  matters. 

Among  the  four  chief  elements  in  plants,  the  only  one 
which  we  have  hot  studied  is: 

CARBON. 

The  Source  of  Carbon  in  Plants.  —  Carbon  dioxide 
is  one  of  the  most  important  substances  in  the  food  of 
plants.  But  the  oxygen  of  this  substance  is  of  no  use 
to  them ;  they  get  enough  of  that  from  other  sources ; 


104 


COMPOSITION    OF  PLANTS. 


it  is  the  carbon  which  is  useful.  Now,  every  leaf  of  a 
growing  plant  is  taking  the  carbon  dioxide  of  the  air 
which  passes  over  it.  We  learned  this  when  studying 
the  subject  of  respiration.  This  substance  is  decomposed 
while  in  the  leaf ;  its  oxygen  is  exhaled,  but  its  carbon 
remains  to  enter  into  combination  as  a  part  of  the  body 
of  the  plant. 

Charcoal-making.  —  This  carbon,  which  the  plant  has 
taken  from  the  atmosphere,  and  also  the  little  which 
it  may  have  taken  up  through  its  roots,  is  obtained  without 


much  difficulty,  for  use  in  the  arts,  and  we  are  acquainted 
with  it  under  the  name  of  charcoal. 

The  charcoal-maker  piles  his  sticks  of  wood  in  the  form 
of  a  mound,  and  covers  the  whole  with  dirt  and  turf.  He 
leaves  a  few  small  holes  for  a  little  air  to  enter  the  pile 


COMPOSITION    OF   PLANTS.  105 

at  the  bottom,  and  another  at  the  top  for  the  smoke  to 
escape,  and  in  this  way  a  half-smothered  burning  is  kept 
up  for  a  long  time,  as  shown  in  Fig.  48. 

Now  what  change  occurs  ?  A  very  simple  one.  The 
wood  is  decomposed  by  the  heat ;  its  gaseous  constituents 
are  driven  away,  but  its  solid  carbon  is  left  behind.  Not 
all  of  it,  to  be  sure,  for  a  little  of  it  unites  with  oxygen 
and  flies  away  as  carbon  dioxide.  But  the  carbon  which 
is  lost  in  this  way  is  very  little  compared  with  the  char- 
coal which  is  left. 

In  appearance,  the  wood  only  seems  to  have  changed  in 
color.  It  is  black.  In  other  things  the  charcoal  looks  like 
the  wood.  There  is  the  bark  with  all  its  knotty  roughness. 
There  are  the  annual  rings  inside  the  bark,  to  be  plainly 
counted,  and,  if  we  look  through  a  microscope,  there  are 
the  delicate  cells,  which  the  microscope  could  have  shown 
us  in  the  wood  before  it  was  burned.  Let  us  lift  it,  and 
it  is  easy  to  feel  that  the  wood  has  lost  much  of  its  weight, 
but  really  it  is  not  easy  to  see  that  it  has  lost  much  of 
its  size ;  the  stick  of  charcoal  is  very  nearly  as  large  as 
the  stick  of  wood  from  which  it  was  made. 

CHARCOAL  is  NOT  QUTTE  PURE  CARBON.  —  When  pure 
carbon  burns  it  is  wholly  changed  into  carbon  dioxide  gas ; 
no  solid  ash  remains,  but  charcoal  always  leaves  a  little 
ash,  which  proves  it  to  be  impure  carbon. 

OTHER  IMPURE  FORMS  RESEMBLTXG  CHARCOAL.  —  Char- 
coal is  only  one  of  the  many  common  forms  of  carbon. 
Among  those  most  nearly  like  charcoal  we  may  mention 
now  the  hard  coal,  which  is  taken  from  mines  for  fuel; 
coke,  the  black  and  porous  solid  left  in  the  retorts  of 
gas-works ;  bone-ldack,  obtained  by  heating  bones  111  close 
vessels ;  soot,  to  be  found  in  chimneys ;  and  /amp-black, 
so  much  used  in  the  manufacture  of  printing-ink. 

Lamp-black.  —  Lamp-black  is   made   by  burning   pitch 


106 


COMPOSITION    OF   PLANTS. 


or  tar  with  little  air.     The  pitch  is  put  into  an  iron  pot 
and  heated  as  shown  at  the  left  in  the  cut  (Fig.  49).     A 

dense  black  smoke 
is  carried  by  the 
draught  over  into 
a  large  chamber.  The 
blackness  of  this 
smoke  is  due  to  fine 
particles  of  carbon. 
This  substance  col- 
lects on  the  Avails  of 
the  chamber,  and  is 
afterwards  taken  out 
as  a  fine  black  powder. 
This  is  lamp-black. 

Printers'  ink    is   a 
mixture     of     lamp- 
black and  oil ;  every 
printed  mark  on  this 
page  is  a  thin  layer 
of     carbon     clinging 
tightly  to  the  paper. 
Action  of  Charcoal  on  Gases — Charcoal  is  very  por- 
ous, and  has  remarkable  power  to  absorb  gases.      Let   us 
study  this  action  by  experiment  with  ammonia. 

Ex.  67.  —  I  must  first  heat  the  charcoal  to  redness  to 
drive  out  the  air  already  in  it.  I  select  a  piece  that  has 
been  well  burned,  make  it  about  one  inch  long,  and  small 
enough  to  slide  easily  into  my  graduated  cylinder.  I  place 
it  in  the  bottom  of  my  porcelain  dish,  or  letter,  in  a  large 
iron  spoon,  cover  it  completely  with  fine  sand,  and  put  it 
in  a  good  fire.  After  it  has  been  heated  to  full  redness 
for  some  time  1  let  it  cool,  still  protected  by  the  sand. 

While  the  spoon  is  cooling  1  fill  my  cylinder  with  am- 
monia gas,  in  this  way : 


COMPOSITION    OF    PLANTS. 


107 


Place  the  cylinder,  inverted,  through  the  ring  of  the  sup- 
port.    Pour  5  cc.  liquid  ammonia  into  the  side-neck  tube, 

and  put  the  delivery 

tube  up  into  the  cyl- 
inder.    Then  gently 

heat   the    liquid.      I 

can  hold  it  by  means 

of  a  strip   of  paper 

which  I  wind  around 

it,  as  shown  in  Fig. 

50.      Ammonia     gas 

will  be   driven    over 

into     the      cylinder, 

and,    being    little 

more    than    half    as  FI-.  50. 

heavy  as  air,  it  will  rise  to  the  top  and  gradually  expel  the 

air  until  the  cylinder  is  filled. 

I  now  place  the  cold  charcoal  in  the  mouth  of  the  cylin- 
der and  then  quickly  lower  it  into  a  dish 
of  mercury.  If  the  mercury  rises  in  the 
cylinder,  as  in  Fig.  51,  it  will  prove  that 
the  ammonia  gas  is  being  absorbed  by  the 
charcoal. 

FACTS.  —  Charcoal  will  take  up  90  times 
its  own  volume  of  ammonia  gas,  but  only 
8  or  9  times  its  volume  of  oxygen  or  nitro- 
gen or  carbon  dioxide.  This  remarkable 
power  of  charcoal  makes  it  very  useful  in 
hospitals  and  other  places  where  offensive 

odors  are  to  be  found.     It  will  absorb  the  bad  gases,  and 

thus  purify  the  air. 

Even  animal  substances,  when  decaying,  lose  their  power 

to  offend  us  by  their  odor,  if  covered  with  a  layer  of  good 

charcoal.     The  decay  will  go  on,  but  the  odor  will  be  lost. 


Fig.  51. 


108 


COMPOSITION    OF   PLANTS. 


Action  of  Charcoal  on  Colors.  —  Charcoal  also  has 
the  power  to  absorb  many  coloring  matters.  Animal  char- 
coal, or  bone-black,  possesses  this  property  in  higher  degree 
than  wood  charcoal. 

Ex.  68.  —  I  prepare  a  filter,  and  rest  the  funnel  in  the 
mouth  of  the  cylinder.  I  fill  the  filter  nearly  full  of  bone- 
black.  Finally,  I  pour  upon  it  some  water  colored  with 
blue  litmus.  If  it  comes  through  still  colored,  I  pour  it 
back  and  let  it  run  through  a  second  time.  Is  the  color 
removed  ?  It  has  been  absorbed  by  the  charcoal. 

Ex.  69.  —  In  the  same  way  I  filter  some  water  colored 
with  cochineal. 

Ex.  70.  —  I  try  a  solution  of  dark  brown  sugar. 
Ex.  71.  —  I  try  a  solution  of  potassium  chromate.     This 
is  a  mineral  coloring-matter ;  the  others  have  been  organic. 
Is  the  color  discharged  in  all  these  cases  ? 
APPLICATION.  —  This  power  of  charcoal  makes  it  very 
useful  for  taking  the  color  out  of  liquids.     Great  quantities 

are  used  to  remove  the 
brown  color  from  crude 
sugar.  After  passing 
the  dark  syrup  through 
a  charcoal-filter  it  is 
bright  and  colorless. 

Charcoal  filters  are 
much  used  to  purify 
drinking-water.  The 

^^MP*--*    a  ^-,^^-iU--      charcoal  gradually  loses 
^^  "7^  its  power  as  its  pores 

Flg  M-  are     more    and    more 

filled  with  the  impurities.  Fresh  portions  should  then  be 
put  in  its  place,  or  the  same  portion  may  be  again  heated 
to  redness,  which  will  restore  its  power. 


COMPOSITION    OF    PLANTS.  109 

Action  of  Charcoal  on  Oxides.  —  Charcoal  has  a  strong 
attraction  for  oxygen,  and  when  very  hot  it  will  decompose 
many  compounds  of  oxygen  in  order  to  unite  with  it. 

Ex.  72.  —  I  make  a  mixture  of  1  g.  copper  oxide  with 
about  its  own  bulk  of  powdered  charcoal,  put  it  into  the 
side-neck  ignition-tube,  and  place  the  end  of  the  delivery 
tube  in  some  lime-water  contained  in  a  test-tube,  as  shown 
in  Tig.  52,  and  then  apply  the  heat  of  the  Bunsen  lamp. 

What  is  the  effect  on  the  lime-water  ? 

What,  then,  was  the  gas  produced  by  the  action  ? 

What  are  the  elements  of  this  gas  ? 

In  what  form  were  these  elements  in  the  mixture  ? 

Can  you  see  any  change  in  the  black  copper  oxide  ? 

What,  then,  must  have  been  the  action  of  the  carbon  ? 

THE  FACTS.  —  The  black  copper  oxide  is  composed  of 
copper  and  oxygen,  but  when  heated  the  carbon  takes  the 
oxygen  away  from  the  copper  and  unites  with  it  to  form 
carbon  dioxide.  This  leaves  the  copper  free.  The  carbon 
dioxide  whitens  lime-water.  The  copper  left  behind  should 
appear  distinctly  reddish  in  the  tube. 

This  power  of  carbon  to  decompose  oxides  makes  it  very 
useful  in  the  work  of  getting  metals  out  of  ores.  Iron,  for 
example,  is  found  in  the  mine  in  the  form  of  iron  oxide, 
and  by  mixing  this  ore  with  coal,  and  then  heating  it 
intensely  in  a  furnace,  its  oxygen  is  taken  away  by  the 
carbon,  and  the  iron  is  left  in  the  metallic  form. 

The  Diamond The  diamond,  most  brilliant  of  gems, 

is  nothing  but  carbon.  It  is  crystallized  carbon.  Dull, 
black  charcoal,  very  common  and  very  cheap,  and  the  beau- 
tiful diamond,  most  costly  of  precious  gems,  are  only  two 
different  forms  of  the  same  element. 

The  diamond  is  the  hardest  known  substance.  It  can- 
not be  cut  or  even  scratched  by  any  other.  Very  small 


110 


COMPOSITION    OF   PLANTS. 


and  otherwise  useless  diamonds   are  set   in   the  end   of  a 
proper  handle  and  are  commonly  used  for  cutting  glass. 

When  found  in  the  earth  the  diamond  has  the  shape  and 
appearance  of  a  roughly  rounded  pebble.  This  rough  gem  is 
"cut"  into  one  of  two  principal  forms  of  jewel.  They  are 
called  the  brilliant  and  the  rose.  The  first  of  these  is  re- 
garded as  the  finest.  Its  shape  is  well  shown  in  Fig.  53. 
t  Ki  Look  at  the  gem  sidewise, 

and  it  appears  as  seen  in 
the  upper  part  of  the  pic- 
ture; look  at  the  top  of 
it,  and  it  appears  as  seen 
in  the  lower  part.  The 
form  of  the  rose  is  seen  in 
Pig.  54 ;  a  side  view  above 
and  a  top  view  below. 

Graphite.  —  Another 
form  of  carbon  is  known 
under  the  common  name  of 
black-lead,  and  is  very  fa- 
miliar to  us  in  its  most 
useful  shape,  the  lead  of 
our  lead-pencils.  This 
name  does  not  belong  to 
it  properly,  for  it  is  not 
lead.  It  has  no  proper- 
ties like  those  of  lead  ex- 
cept that  which  allows  it 
to  leave  marks  upon  paper.  It  is  sometimes  called  plum- 
bago; but  the  name  by  which  it  is  generally  known  in 
chemistry  is  graphite. 

Graphite. is  found  in  the  earth.  It  is  as  black  as  coal, 
but  it  has  a  dull  shining  appearance,  which  coal  has  not. 
It  is  among  the  softest  minerals  to  be  found,  and  as  per- 


Fig.  53. 


COMPOSITION    OF   PLANTS.  Ill 

fectly  opaque  as  can  be.     How  unlike  the  hard  and  trans- 
parent diamond  in  these  respects  ! 

THREE  FORMS  OF  THE  SAME  ELEMENT.  —  All  three  of 
these  forms  of  carbon  are  alike  in.  some  respects.  No  fire 
can  melt  them.  No  liquid  can  dissolve  them,  if  we  except 
melted  iron,  which  seems  to  dissolve  a  little  carbon.  They 
cannot  be  changed  by  exposure  to  the  atmosphere ;  they 
suffer  no  decay,  no  rust.  But  let  them  be  heated  hot 
enough,  where  oxygen  is 
present,  and  they  will  burn, 
and  the  experiment  shows 
that  they  are  not  only  much 
alike  in  some  respects,  but 
that  they  are  actually  the 
same  kind  of  matter. 

For  we  have  proved  by 
experiment,  that  when  char- 
coal burns  carbon  dioxide  is 
produced.  By  heating  the 
diamond  to  a  white  heat,  in 
oxygen  gas,  it  will  be  con- 
sumed, and  carbon  dioxide 
will  be  found  in  its  place. 
Graphite  has  also  been  FiJ  64> 

burned,  and  the  same  substance,  carbon  dioxide,  produced 
by  its  combustion. 

Now  we  know  that  it  takes  carbon  and  oxygen  always, 
and  nothing  else,  to  make  carbon  dioxide.  The  carbon 
must  come  from  the  fuel  which  burns.  Hence  charcoal, 
diamond,  and  graphite  are  all  the  same  element,  —  carbon. 

What  other  element  have  we  found  to  exist  in  more  than 
one  form  ?  What  name  is  given  to  this  property  of  ele- 
ments ? 

How  this  element  has  come  to  be  in   such  wonderfully 


112 


COMPOSITION    OF   PLANTS. 


different  forms  we  cannot  tell.  No  chemist  can  change 
charcoal  into  diamond,  nor  can  any  one  tell  us  how  it  has 
been  done  in  the  great  laboratory  of  nature. 

CARBON    DIOXIDE. 

Preparation.  —  Carbon  dioxide  is  the  chief  compound  of 
carbon  and  oxygen.  It  is  most  easily  obtained  by  the 
action  of  hydrochloric  acid  on  marble. 

Ex.  73.  —  My  apparatus  is  much  the  same  as  that  used 
in  making  oxygen  (Ex.  23).  It  is  shown  in  Fig.  55.  A 

little  lime-water  is 
placed  in  the  bottle 
d,  and  clear  water 
in  a,  enough  to 
cover  the  end  of  the 
glass  tube.  The 
conical  flasks  are 
joined  by  rubber 
tubes,  the  long  tube 
in  each  to  the  short 
tube  of  the  one  be- 
fore it,  and  then 
rl«-  "•  the  long  tube  of  a 

to  the  side-neck  of  the  flask  s.  The  joints  are  all  air-tight. 
I  put  about  10  g.  of  marble  in  small  pieces  into  the  side- 
neck  flask  and  pour  upon  it  about  25  cc.  of  dilute  hydro- 
chloric acid,  half  water,  and  at  once  close  the  flask  with  its 
stopper.  The  gas,  making  in  s,  will  drive  the  air  before  it 
all  out  at  d.  The  flame  of  a  burning  splinter  thrust  into  d 
will  tell  when  the  bottle  is  full  of  the  carbon  dioxide. 
Then  exchange  this  bottle  for  another  having  some  blue 
litmus-water  instead  of  lime-water. 

If  the  gas  begins  to  come  too  slowly,  I  may  remove  the 
cork  of  «,  add  more  acid,  and  replace  it.  Now  consider 
the  following  things: 


COMPOSITION    OF   PLANTS. 


113 


Fig.  56. 


Describe  the  action  which  took  place  in  s. 
What  effect  was  produced  in  the  lime-water  ? 
What  is  the  effect  of  this  gas  on  flame  ? 
What  is  the  effect  of  it  on  blue  litmus  ? 
Why  does  the  gas  stay  in  the  open  bottle  ? 
Ex.  74-  —  What  if  the  vessel  of  carbon  dioxide  is  open 
downward  ?     I    remove     the     tubes 
and  cork   from  flask  c,  Fig.  55,  and 
then  hold  the  flask's  mouth  upon  the 
lip  of  a  small  wide-mouth  bottle,  as 
if  to  pour  the  gas,  as  shown  in  Fig. 
56.     After  a  minute  I  place  the  flask 
upon  the  table  and  plunge  the  flame 
of  a  splinter   down   into  the   bottle, 
and   afterward   into   the  flask.     The 
flame   shows  that  the  gas  was  actu- 
ally poured,  like  water,  from  c  into  the  bottle. 

Ex.  75.  —  Is  this  gas  soluble  in  water?  The  gas  bub- 
bled through  the  water  in  a,  Fig.  55,  and  I  test  that  water 
to  see  whether  there  is  carbon  dioxide 
in  it.  I  put  some  lime-water  in  a  test- 
tube,  and,  after  taking  the  rubber  tubes 
from  a,  I  lift  the  flask  and  pour  water 
from  it  into  the  lime-water,  as  shown  in 
Fig.  57. 

If  the  water  in  a  has  dissolved  carbon 
dioxide,  the  lime-water  will  be  whitened. 

DESCRIPTION.  —  Carbon  dioxide  is  a  compound  of 
carbon  and  oxygen:  this  was  proved  by  Ex.  26.  We 
see  that  it  is  a  colorless  gas,  and  much  heavier  than  air 
(Exs.  73,  74).  In  fact  it  is  about  one  and  one-half  times 
heavier  than  air  (1.529).  It  whitens  lime-water  by  com- 
bining with  the  lime  and  making  the  white  solid  called 
calcium  carbonate,  which  the  water  cannot  dissolve,  and  it 


Fig.  57. 


114  COMPOSITION    OF    PLANTS. 

reddens  blue  litmus-water  (Ex.  73),  for  a  reason  which  will 
appear  by  and  by. 

This  gas  will  put  out  a  fire  (Ex.  73)  just  as  quickly  as 
will  water,  and  for  the  same  reason.  A  body  will  not  burn 
without  oxygen,  and  when  covered  with  water  the  oxygen 
of  the  air  cannot  get  to  it.  So  when  in  carbon  dioxide,  no 
oxygen  can  reach  the  body,  and  the  fire  dies. 

So,  too,  this  gas  will  cause  death,  just  as  will  water.  An 
animal  must  have  oxygen  to  breathe,  or  it  must  die.  It 
drowns  in  water  because  water  keeps  the  air  away  from 
its  lungs;  carbon  dioxide  will  do  the  same  thing.  There 
is  too  little  of  this  gas  in  the  open  air  to  do  harm,  but 
where  it  collects  in  large  quantities  an  animal  dies  because 
it  can  get  too  little  oxygen  to  keep  it  alive. 

It  sometimes  collects  in  mines,  and  the  miners  call  it 
ckoke-damj).  It  sometimes  collects  in  wells,  and  makes 
them  dangerous  to  enter ;  a  lighted  candle  will  tell  a  work- 
man whether  this  gas  is  present  in  dangerous  quantities. 
It  often  collects  in  school-rooms  and  churches  and  other 
unventilated  houses,  but  not  often  enough  of  it  to  do  much 
harm.  The  truth  is  that  the  breath  of  people  is  full  of 
other  gases,  some  of  which  are  very  poisonous,  and  the 
mischief  in  unventilated  rooms  is  done  by  these  compan- 
ions of  the  carbon  dioxide  instead  of  by  this  gas  itself. 

Carbon  dioxide  is  soluble  in  water  (Ex.  75).  It  is  found 
that  water  will  usually  dissolve  about  its  own  volume.  But, 
like  all  gases,  more  will  dissolve  in  colder  water,  and  still 
more  when  under  greater  pressure.  Nearly  all  water  con- 
tains this  gas,  but  the  quantity  in  solution  is  generally 
small.  In  some  springs,  however,  it  is  very  abundant.  It 
is  so  in  the  noted  mineral  springs  of  Saratoga.  And  the 
refreshing  summer  drink  —  soda-water  —  is  nothing  but 
water  charged  with  a  large  quantity  of  this  gas  which  has 
been  forced  into  it  by  great  pressure. 


COMPOSITION    OF   PLANTS.  115 

Carbon  Monoxide Besides  carbon  dioxide  there  is 

another  compound  of  carbon  and  oxygen  called  carbon 
monoxide.  See  p.  82.  It  is  a  colorless  gas.  It  takes  fire 
easily,  and  burns  with  a  pale  blue  flame ;  this  is  the  flame 
which  is  often  seen  playing  over  the  surface  of  a  new- 
made  coal-fire.  When  the  coal  burns  at  the  bottom  of 
the  grate  it  produces  carbon  dioxide,  as  usual,  but  as  this 
carbon  dioxide  goes  up  through  the  hot  coal  above  it 
gives  up  a  part  of  its  oxygen  and  becomes  carbon  mon- 
oxide. And  then  when  this  monoxide  comes  out  into  hot 
air,  at  the  surface,  it  takes  oxygen  and  becomes  carbon 
dioxide  again. 

This  gas  is  very  likely  to  escape  being  burned.  There 
may  not  be  air  enough,  or  there  may  not  be  heat  enough 
to  burn  it.  This  should  be  remembered  when  coal  is 
used  for  warming  rooms,  for  carbon  monoxide  is  a  very 
poisonous  gas.  Accidents  have  many  times  happened 
from  burning  charcoal  in  open  fires  with  poor  draught. 
This  poisonous  gas  escaping  into  the  room  destroys  life. 

COMPOSITION  OF  THE  TWO  OXIDES.  —  It  is  found  by 
analysis  of  the  two  gases  that  the  carbon  monoxide  con- 
tains just  one-half  as  much  oxygen  as  the  carbon  dioxide. 
The  proportions  are  as  follows  : 

In  carbon  monoxide  there  are  16  of  O  combined  with  12  of  C 
dioxide        "       "    32  "  O          "  "     12  "  C 

What  law  does  this  illustrate  ? 

Compounds  of  Carbon  and  Hydrogen.  —  No  other  ele- 
ments form  so  many  compounds  with  one  another  as  do 
carbon  and  hydrogen.  Of  carbon  and  oxygen  there  are 
only  two.  Of  nitrogen  and  oxygen  there  are  five,  and 
this  is  rather  an  unusual  number  for  two  elements  only. 
But  of  carbon  and  hydrogen  the  compounds  are  many 
scores  in  number.  They  are  called  hydrocarbons.  Just 
now  we  will  study  only  one  of  these. 


116  COMPOSITION    OF  PLANTS. 

Methane — This  is  the  simplest  one  of  the  hydrocar- 
bons. It  is  commonly  called  marsh-gas,  which  is  a  very 
appropriate  name,  because  it  is  abundant  in  marshy 
places.  Have  you  never  seen  the  water  of  ponds  and 
quiet  pools  stirred  by  bubbles  of  gas  breaking  at  the  sur- 
face ?  It  is  a  very  common  thing  to  be  seen  in  water 
standing  over  muddy  bottoms.  The  bubbles  are  of  marsh- 
gas.  They  are  set  free  by  the  decay  of  vegetable  sub- 
stances in  the  mud  below. 

Marsh-gas  flows  from  coal-beds  into  the  mines  where 
the  laborers  are  at  work.  The  most  awful  effects  are 
then  sometimes  produced  by  it.  It  is  very  combustible, 
and,  more  than  this,  when  mixed  with  air  it  is  terribly 
explosive.  Fancy  it  flowing  into  a  mine,  mixing  with  the 
air  around  the  miners,  and  the  mixture  then  touching 
the  flame  of  the  miner's  lamp!  The  lamps  and  the  lives 
of  the  miners  are  then  extinguished  at  once  by  a  terrible 
explosion. 

The  miners  have  given  this  gas  the  name  of  fire-damp. 

It  is  found  by  analysis  that  methane  is  made  of  carbon 
and  hydrogen  only,  and  in  quantities  by  weight  which  are 
as  12  to  4. 
In  methane  there  are  12  parts  of  C  combined  with  4  parts  of  H. 

How  many  combining  weights  of  carbon  in  the  12  of  C  ? 
How  many  combining  weights  of  hydrogen  in  the  4  of 
H? 


ELEMENTS,    MOLECULES,    AND    ATOMS. 

The  Number  of  the  Elements We  have  already 

seen,  p.  24,  that  an  element  is  a  substance  which  has  never 
yet  been  decomposed. 

At  present  (July,  1886)  seventy-one  elements  are  known. 
Some  of  these  have  been  discovered  very  lately,  and  per- 
haps others  may  be  found  in  the  future.  On  the  other 
hand  some  so-called  elements  have  been  found  to  be  com- 
pounds, and  it  may  be  that  some  of  the  seventy-one  shall 
yet  be  decomposed.  All  that  we  can  say  is  that  there  are 
seventy-one  kinds  of  matter  which  chemists  to-day  are  not 
able,  by  any  means  in  their  power,  to  break  into  simpler 
bodies.  As  out  of  twenty-six  letters  of  the  alphabet  all 
the  words  in  the  English  language  are  made,  so  out  of 
these  seventy-one  elements  all  the  compounds  in  nature 
are  formed. 

But  only  a  few  of  this  small  number  are  at  all  abundant. 
In  fact,  the  larger  part  of  the  earth,  and  all  it  contains,  is 
made  up  of  only  about  a  dozen  elements.  All  the  water  on 
the  globe  consists  of  oxygen  and  hydrogen.  Four-fifths  of 
the  air  is  nitrogen.  These  three,  with  carbon,  make  up  by 
far  the  larger  part  of  all  plants,  and  the  bodies  of  animals. 
And  as  for  rocks  and  soils,  they  consist  chiefly  of  those 
just  named,  with  eight  others, — sulphur,  silicon,  potas- 
sium, sodium,  calcium,  magnesium,  aluminum,  and  iron. 
With  these  exceptions,  the  elements  are  not  common,  and 
one-third  of  the  whole  number  are  very  rare. 

The  names  of  all  the  elements  now  known  are  given  in 
the  following  table.  The  symbols  and  atomic  weights 
will  be  explained  soon. 

117 


118 


ELEMENTS,    MOLECULES,    AND    ATOMS. 


THE    SEVENTY-ONE    ELEMENTS. 


— 

NAMES. 

Symbols. 

Atomic 
Weights. 

NAMES. 

Symbols. 

Atomic 
Weights. 

Aluminum  .    . 

Al. 

27.3 

Molybdenum    . 

Mo. 

96. 

Antimony   ,    \ 

Sb. 

120. 

Nickel     ... 

Mi. 

58. 

Arsenic  .    .    . 

As. 

75.    • 

Nitrogen  .    .    . 

N. 

14. 

Barium    .     .     . 

Ba. 

137. 

Osmium  .    .    . 

Os. 

198.6 

Beryllium  (')    . 

Be. 

9.    . 

Oxygen    .    .    . 

0. 

16. 

Bismuth  .     .    . 

Bi. 

208. 

Palladium    .    . 

Pd. 

106. 

Boron      .    .    . 

B. 

11.    . 

Phosphorus 

P, 

31. 

Bromine  .    .    . 

Br. 

80. 

Platinum     .    . 

Pt. 

195. 

Cadmium    .  V  .J 

Cd. 

112. 

Potassium   .    . 

K. 

39.1 

Csesium  .    .    . 

Cs. 

1*3. 

Rhodium     .    . 

Rh. 

104. 

Calcium  .    .    ,l 

Ca. 

40. 

Rubidium    .    . 

Rb. 

85.5 

Carbon    .    .    . 

C. 

12. 

Ruthenium.    . 

Ru. 

103.5 

Cerium    .    .    . 

Ce. 

141. 

Samarium   .    . 

Sin. 

150. 

Chlorine  .    .    . 

Cl. 

35.5 

Scandium    .    . 

Sc. 

44. 

Chromium  .     . 

Cr. 

52. 

Selenium     .    . 

Se. 

79. 

Cobalt     .    .    . 

Co. 

69. 

Silicon     .    .    . 

Si. 

28. 

Columbium  (2)  . 

Cb. 

94. 

Silver.    .    .    . 

Ag. 

108. 

Copper    .    .    . 

Cu. 

63.3 

Sodium    .    .    . 

Na. 

23. 

Decipium    .    . 

Dp. 

? 

Strontium    .    . 

Sr. 

87.5 

Didymium  (3)  . 

Di. 

142.3^ 

Sulphur  .    .    . 

S. 

32. 

Erbium   .    .    , 

Er. 

106. 

Tantalum    .    . 

Ta. 

182. 

Fluorine  .    .    . 

F. 

19. 

Tellurium    .    . 

Te. 

125. 

Gallium  .    .    . 

-Ga. 

69. 

Terbium  .    .    . 

Tb. 

? 

Germanium.    . 

Gr 

72.75? 

Thallium     .    . 

Tl. 

204. 

Gold    .... 

An. 

196.5 

Thorium  .    .    . 

Th. 

232. 

Hydrogen    .    . 

H. 

1. 

Thulium  .    .    . 

Tm. 

i 

Indium    .    .    . 

In. 

113.6 

Tin      .... 

Sn. 

118. 

Iodine     .    .    . 

I. 

127. 

Titanium     .     . 

Ti. 

48. 

Iridimu   .    .    , 

Ir. 

193. 

Tungsten  (4)      . 

W. 

184. 

Iron    .... 

Fe. 

56. 

Uranium.    .    . 

U. 

240. 

Lanthanum 

La. 

138.2 

Vanadium  .    . 

V. 

51.2 

Lead   .    .    .    . 

Pb. 

207. 

Ytterbium   .    . 

Yb. 

178. 

Lithium  .    .    . 

Li. 

7. 

Yttrium  .    .    . 

Yt. 

89. 

Magnesium  .    . 

Mg. 

24. 

Zinc    .... 

Zn. 

65. 

Manganese  .    . 

Mn. 

55. 

Zirconium  .    . 

Zr. 

90. 

Mercury  .    .    . 

Hg- 

200. 

(')  Beryllium  is  also  called  Glucinum,  with  the  symbol  Gl. 

(2)  Columbian!  is  also  called  Niobium,  with  the  symbol  Nb. 

(3)  The  announcement  ha*  come  from  Vienna  that  Didymium  lias  been  decom- 
posed.   See  Chemical  News,  vol.  52,  and  Nature,  vol.  3'J,  p.  435. 

(4)  Tungsten  has  also  been  called  Wolt'ramiuiu. 


ELEMENTS,    MOLECULES,    AND    ATOMS.  119 

The  Three  Forms  of  Matter Earth,  water,  and  air 

represent  the  solid,  liquid,  and  gaseous  forms  of  matter. 
So  far  as  we  know,  all  kinds  of  matter  are  in  one  or  another 
of  these  three  conditions.  But  ice  and  water  and  steam 
are  all  one  kind  of  matter,  and  yet  one  is  a  solid,  another 
is  a  liquid,  and  another  a  gas. 

Ice,  when  heated,  melts  into  water,  and  water  when 
heated  to  a  higher  temperature  boils  into  steam.  We 
tind  that  many  other  solids  are  like  ice  in  this  respect  — 
they  melt  when  heated,  and  that  other  liquids  are  like 
water  —  they  may  be  changed  into  vapor  by  heat. 

These  are  facts.  We  know  them  to  be  so,  because  we 
have  seen  these  changes  happen  over  and  over  again. 
Indeed,  so  many  substances  have  been  tried  and  found  to 
be  solid  at  low  temperature,  liquid  at  some  higher  tempera- 
ture, and  gaseous  at  some  temperature  higher  still,  that 
we  feel  quite  sure  that  the  facts  are  the  same  for  all ;  and 
so  we  say  that 

The  solid,  liquid,  and  gaseous  forms  of  matter  depend  on 
the  amount  of  heat  in  them. 

This  one  statement,  made  out  of  many  facts,  is  a  law. 

Another  Effect  of  Heat If  we  warm  a  piece  of 

iron  it  will  become  larger,  and  if  we  cool  it  it  will  become 
smaller.  The  same  thing  is  true  of  a  piece  of  wood ;  it  is 
larger  when  it  is  hot  than  when  it  is  cold.  A  given  weight 
of  water,  or  of  air,  is  found  to  be  larger  and  larger  as  it  is 
heated  more  and  more.  These  are  facts.  They  have  been 
proved  to  be  true  of  the  substances  named,  and  of  a  great 
many  more  beside.  Now  let  us  put  all  such  facts  together 
into  one  statement  by  saying  that 

Heat  makes  a  body  larger  without  changing  its  weight. 

This  is  a  law.  A  law,  in  science,  is  simply  a  single 
statement  which  covers  a  large  number  of  facts. 


120  ELEMENTS,    MOLECULES,    AND   ATOMS. 

THE  REASON.  —  A  body  is  larger  when  it  is  hot ;  can 
we  tell  why  it  is  so  ?  Nobody  knows  with  absolute  cer- 
tainty why  bodies  should  expand  when  heated.  But  the 
best  way  to  account  for  it  is  to  suppose  that  matter  is 
made  up  of  very  small  particles  which  are  quite  separate 
from  one  another,  so  that  they  may  be  driven  farther  apart 
or  crowded  nearer  together.  Heat  drives  them  farther 
apart  and  makes  them  till  more  space,  and  cold  allows 
them  to  fall  more  closely  together,  and  thus  to  fill  a  smaller 
space.  Surely  this  is  a  very  good  reason  why  heat  should 
make  a  body  larger,  and  cold  should  make  it  smaller.  If  a 
body  were  made  up  of  separate  particles  it  would  behave 
just  as  we  see  that  it  does  behave  when  heated  and  cooled, 
and  so  we  may  suppose  that  it  is  made  up  of  such  particles. 
Perhaps  it  is  so. 

If  we  imagine  every  body  to  be  made  up  of  small  parti- 
cles which  are  quite  separate,  we  can  understand  many 
other  facts  beside  expansion  by  heat.  Take,  for  example, 
the  fact  that  you  make  an  india-rubber  ball  smaller 
when  you  squeeze  it.  If  we  are  right  in  supposing  that 
the  ball  is  made  up  of  a  great  multitude  of  small,  separate 
particles,  the  hand  would  make  it  smaller  by  crowding 
them  closer  together.  The  ball  acts  just  (ts  if  it  were  made 
up  of  separate  particles.  Probably  it  is  so. 

In  a  great  many  other  ways  bodies  behave  exactly  as  if 
they  were  made  up  of  such  separate  particles.  Indeed,  so 
i'ar  as  they  have  been  examined,  the  facts  are  always  just 
what  we  should  expect  if  matter  be  made  up  of  small  par- 
ticles which  are  some  distance  apart.  On  this  account  we 
believe  it  to  be  so. 

Now,  something  which  is  believed  because  it  gives  good 
reasons  for  a  large  number  of  facts  is  called  a  theory. 
That  all  bodies  are  made  up  of  minute  particles  which  do 
not  touch  one  another  is  our  theory  of  matter. 


ELEMENTS,    MOLECULES,    AND    ATOMS.  121 

The  student  cannot  too  early  nor  too  carefully  fix  in  his 
mind  the  difference  between  facts  and  theories.  Facts  are 
things  known  to  be  true ;  theories  are  things  believed  to  be 
true. 

Molecules.  —  According  to  the  theory  of  matter  just 
stated,  all  bodies  are  made  up  of  separate  particles.  These 
particles  cannot  be  seen.  They  are  so  small  as  to  be 
quite  beyond  our  sight  with  the  best  microscope.  They 
are  the  very  smallest  pieces  of  a  substance  which  can  pos- 
sibly exist,  so  that  to  divide  them  into  parts  will  change 
the  substance  into  something  else.  They  are  called  mole- 
cules. A  molecule  is  a  particle  of  substance  so  small  that 
it  cannot  be  divided  without  changing  the  nature  of  the 
substance.  Molecules  of  the  same  substance  are  all  alike, 
but  the  molecules  of  different  kinds  of  matter  are  not  alike. 

Some  Facts  about  the  Expansion  of  Gases — It  has 
been  found  by  very  careful  and  repeated  experiments  that 
if  we  take  273  cc.  of  air  as  cold  as  freezing  water,  0°  C. 
and  warm  it  just  1°  C.,  it  will  become  just  274  cc.  Add 
another  degree  of  heat  and  it  will  become  275  cc.,  and  so 
on,  each  degree  of  heat  expanding  it  just  1  cc.  In  other 
words,  one  degree  of  heat  will  always  expand  air  just 
27TT  °f  what  its  volume  is  at  0°  C. 

The  rate  has  been  found  also  for  many  other  gases,  and 
it  is  the  same  for  all.  This  is  a  very  important  fact.  It 
is  not  so  among  solids  and  liquids ;  no  two  solids  expand 
exactly  alike ;  no  two  liquids.  Why  do  all  gases  expand 
alike  when  heated,  while  solids  and  liquids  do  not  ? 

Again,  if  air  is  pressed  in  a  close  vessel  it  will  be 
crowded  into  smaller  volume ;  but,  on  the  other  hand,  if 
we  put  less  pressure  on  it  the  air  will  expand.  Other 
gases  behave  in  the  same  way.  And  the  same  change  of 
pressure  will  change  the  volume  of  one  just  exactly  as 
much  as  another.  This  is  another  important  fact.  It  is 


122  ELEMENTS,    MOLECULES,    AND    ATOMS. 

not  a  fact  for  solids  and  liquids  ?  Why  should  the  same 
pressure  condense  all  gases  exactly  alike ;  and  the  removal 
of  the  same  pressure  expand  all  gases  exactly  alike  ? 

The  Theory.  —  These  and  other  facts  led  Avogadro,  in 
1811,  to  suppose  that  when  two  gases  are  equally  warm, 
and  under  the  same  pressure,  a  cubic  inch  of  one  contains 
just  as  many  molecules  as  a  cubic  inch  of  the  other.  And 
since  all  gases  behave,  in  so  many  respects,  just  as  they 
would  be  expected  to  do  if  this  famous  hypothesis  were 
true,  it  is  believed  to  be  as  Avogadro  supposed. 

Equal  volumes  of  all  gases,  at  the  same  temperature  and 
pressure,  contain  the  same  number  of  molecules. 

This  is  Avogadro's  theory :  but  it  is  often  called  Avo- 
gadro's  law. 

Chemical  Changes  are  Changes  in  the  Molecules.— 
When  water  is  decomposed  by  electricity  (Ex.  37)  it  is 
broken  into  two  parts ;  one  part  is  hydrogen,  the  other  is 
oxygen.  The  change  is  believed  to  take  place  in  each  sep- 
arate molecule.  When  mercuric  oxide  is  heated  (Ex.  5) 
every  molecule  of  it  is  broken  into  two  parts ;  one  is  mer- 
cury, the  other  oxygen.  When  marble  and  hydrochloric 
acid  act  (Ex.  73)  every  molecule  of  these  two  substances 
is  broken  into  two  parts,  and  then  those  parts  fall  together 
again,  in  a  different  way,  and  make  the  molecules  of  two 
new  kinds  of  matter. 

Atoms.  —  Now  what  shall  we  call  the  smaller  particles 
in  a  molecule  ?  They  are  atom.s.  These  are  the  very 
smallest  pieces  of  matter  that  take  part  in  a  chemical 
change.  They  cannot  be  divided  by  any  known  process 
whatever.  All  bodies  are  made  up  of  molecules,  and  mole- 
cules are  made  up  of  atoms. 

If  the  atoms  of  a  molecule  are  alike,  the  substance  is 
an  element,  but  if  the  atoms  in  a  molecule  are  not  all  alike 
the  substance  is  a  compound. 


ELEMENTS,    MOLECULES,    AND    ATOMS.          123 

The  Explanation  of  the  Law  of  Multiple  Propor- 
tions  The  law  of  multiple  proportions  is  the  statement 

of  a  fact.  We  know  that  the  combining  weight  of  an  ele- 
ment is  never  divided  in  chemical  changes ;  can  we  tell  why  ? 

The  most  natural  reason  is  found  by  supposing  the 
combining  weight  to  be  the  weight  of  a  particle  of  mat- 
ter which  cannot  be  divided,  that  is,  of  an  atom.  Such 
particles  will  pass  unbroken  from  one  kind  of  compound 
into  another.  One  of  them  may  go  alone,  or  some  whole 
number  of  them  may  go  together.  The  weight  of  one  of 
them  is  the  combining  weight  of  the  element,  and  of  any 
whole  number  of  them,  is  a  multiple  of  that  combining 
weight.  And  so  — 

If  jone  element  combines  with  another,  in  more  pro- 
portions than  one,  these  proportions  must  be  multiples  of 
its  combining  weight. 

The  Atomic  Theory.  —  This  theory  of  matter  is  known 
as  the  Atomic  Theory.  Its  main  points  are  these :  All 
bodies  are  made  up  of  molecules,  and  molecules  are  made 
up  of  atoms.  All  chemical  changes  are  changes  in  the 
arrangements  of  the  atoms,  and  the  combining  weights 
of  the  elements  are  the  relative  weights  of  their  atoms. 

The  theory  of  atoms  was  first  proposed  in  1808  by  John 
Dalton.  He  was  the  first  to  see  clearly  that  the  combi- 
nation of  the  elements,  in  definite  and  in  multiple  pro- 
portions, are  facts  which  seem  to  show  that  there  are 
particles  of  matter  which  cannot  be  divided.  The  atomic 
theory  was  made  to  explain  these  laws  of  combination,  and 
it  is  well  fixed  in  chemistry,  because  it  not  only  explains 
these,  but  has  been  found  to  explain  new  facts,  as  fast  as 
they  have  been  discovered,  down  to  the  present  time. 

Symbols  of  Elements Instead  of  writing  the  full 

name  of  the  element  hydrogen,  we  may  simply  write 
the  first  letter,  H,  to  represent  it.  H  is  then  called  the 


if 


124          ELEMENTS,    MOLECULES,    AND    ATOMS. 

symbol  of  hydrogen.  In  the  same  way  0  is  the  symbol  of 
oxygen,  N  of  nitrogen,  and  C  of  carbon. 

Sometimes  the  names  of  two  or  more  elements  begin 
with  the  same  letter,  as  carbon,  calcium,  and  copper.  In 
this  case  a  small  letter  is  used  with  the  large  initial,  thus : 
the  symbol  of  calcium  is  Ca,  and  that  of  copper  is  Cu. 
The  latter  is  from  the  Latin  name  of  copper,  which  is 
Cuprum.  A  symbol  represents  the  name,  and  also  just 
one  atom  of  an  element. 

Formulas  of  Compounds.  —  Instead  of  writing  the  full 
name  mercuric  oxide,  we  may  simply  write  the  symbols 
of  the  elements  of  this  compound,  side  by  side,  Hg  for 
mercury  and  0  for  oxygen,  making  HgO  to  represent  it. 
Hg  O  is  then  called  the  formula  for  mercuric  oxide.  H  Cl 
is  the  formula  for  hydrochloric  acid. 

The  formula  of  a  compound  represents  one  molecule  of  it. 

H2  0  is  the  formula  for  water ;  the  small  figure  2  means 
that  there  are  two  atoms  of  hydrogen  combined  with  one 
of  oxygen  in  the  molecule.  C  02  is  the  formula  for  carbon 
dioxide,  and  shows  that  one  molecule  contains  one  atom 
of  carbon  and  two  atoms  of  oxygen.  H2  S  04  is  the  formula 
for  sulphuric  acid  ;  what  does  it  show  ?  3  H2  S  O4  means 
three  molecules  of  sulphuric  acid,  and  2H2O  means  two 
molecules  of  water.  Notice  the  different  meaning  of 
figures  placed  before  the  formulas  and  those  placed  at  the 
right  and  a  little  below  the  symbols,  in  the  formula. 

In  reading  symbols  and  formulas,  the  names  of  the  sub- 
stances, and  not  the  letters  used,  should  always  be  given. 
We  should  use  symbols  and  formulas  to  shorten  writing, 
but  not  to  shorten  speech. 

Atomic  Weights.  —  We  have  learned  that  hydrochloric 
acid  contains  35.5  times  as  much  chlorine  as  hydrogen  ;  we 
may  say  this  of  any  quantity ;  it  is  true  of  one  molecule, 
which  contains  one  atom  of  chlorine  and  one  of  hydrogen. 


ELEMENTS,    MOLECULES,    AND    ATOMS.          125 

These  numbers,  1  and  35.5,  are  called  the  atomic  weights 
of  hydrogen  and  chlorine,  because  they  are  supposed  to 
represent  the  relative  weights  of  the  atoms  of  these  two 
elements.  We  have  no  idea  how  much,  or  rather  how 
little,  the  atom  of  hydrogen  really  weighs,  but  we  do  be- 
lieve that,  whatever  it  does  weigh,  the  atom  of  chlorine 
weighs  35.5  times  as  much.  We  cannot  tell  the  weight 
of  either,  in  fractions  of  a  gram  or  ounce,  but  we  can  call 
the  weight  of  the  hydrogen  atom  1,  without  saying  what, 
and  then  we  can  say  that  an  atom  of  chlorine  weighs  35.5. 

These  numbers  are  the  same  as  those  which  have  been 
called  combining  weights,  p.  98.  We  know  that  they  are  the 
smallest  relative  weights  of  these  elements  which  combine ; 
this  is  a  fact  discovered  by  experiment.  It  is  believed  that 
they  represent  the  weights  of  the  atoms  of  these  elements. 
This  is  a  part  of  the  atomic  theory. 

And  now  we  see  that  the  symbol  of  an  element  not 
only  represents  one  atom,  but  also  one  atomic  weight. 

Molecular  "Weights —  If  a  molecule  is  made  of  atoms 
we  can  find  its  weight  by  adding  the  weights  of  its  atoms 
together.  There  are  three  atoms  in  a  molecule  of  water, 
H20,  two  of  hydrogen  and  one  of  oxygen.  The  weight 
of  an  atom  of  hydrogen  is  1,  and  of  an  atom  of  oxygen 
is  16,  and  the  weight  of  all  three  atoms  together  must  be 
18.  The  molecular  weight  of  water,  H2  0,  is  therefore  18. 
It  is  not  18  grams,  nor  18  grains,  but  simply  18  times  as 
much  as  the  weight  of  an  atom  of  hydrogen. 

The  atomic  weights  are  given  in  the  table  on  p.  118,  and 
these  will  enable  one  to  find  the  molecular  weight  of  any 
substance  whose  formula  is  known.  Try  it  in  the  follow- 
ing examples. 

What  is  the  molecular  weight  of  hydrochloric  acid,  HC1?     £ 

"  "          "                "            sodium  chloride,  NaCl?      4" 

"  "          "                "            mercuric  oxide,  Hg  O  ?   j£ 

"  "          "                "            sulphuric  acid,  H2SO4?    a  $ 


126  ELEMENTS,    MOLECULES,    AND    ATOMS. 

Reactions.  —  Chemical  changes  are  also  called  reactions. 
Now  chemical  changes  are  changes  in  the  molecules  of  sub- 
stances, and  we  can  show  what  they  are  by  making  changes 
in  the  formulas  which  represent  the  molecules.  In  this 
way  symbols  and  formulas  are  a  great  help  in  the  study 
of  experiments. 

For  example,  suppose  we  wish  to  know  all  about  the 
reaction  of  •  sodium  and  hydrochloric  acid.  We  must 
begin  by  making  the  experiment.  We  may  then  study 
the  results  by  the  help  of  symbols  and  formulas. 

REACTION  OF  SODIUM  AND  HYDROCHLORIC  ACID.  Ex. 
76.  —  I  measure  2  cc.  of  strong  hydrochloric  acid  into  a 
test-tube  which  stands  in  the  rack,  drop  in  upon  it  a  piece 
of  sodium  as  large  as  a  small  pea,  and  loosely  cover  the 
mouth  of  the  tube  with  a  piece  of  paper.  After  half  a 
minute,  I  push  the  flame  of  a  lighted  match  down  into 
the  tube.  When  the  sodium  has  disappeared,  I  drop  in 
another  piece  of  about  the  same  size. 

What  gas  is  set  free  by  the  chemical  action  ? 

What  proof  is  seen  that  another  substance  is  produced  ? 

To  find  out  what  is  this  second  product,  I  first  let  it 
settle  to  the  bottom  of  the  tube,  and  then  pour  off  the 
liquid  so  carefully  that  I  leave  the  solid  behind  almost  dry. 
In  this  way  I  get  rid  of  most  of  the  acid  which  was  not 
decomposed.  I  then  add  three  or  four  cubic  centimeters 
of  water,  to  dissolve  the  white  solid,  pour  the  solution 
into  a  small  porcelain  dish,  and  heat  it  over  a  small  flame 
until  the  water  is  all  driven  off  and  the  solid  remains  dry 
and  white.  The  dish  must  now  stand  until  cold,  after 
which  I  add  a  few  drops  of  water  in  which  the  white  solid 
again  dissolves.  By  tasting  this  liquid  you  may  learn 

What  is  this  second  product  of  the  chemical  action. 

We  have  now  got  the  facts  about  the  reaction  we  are 
studying.  To  get  the  facts  is  always  the  first  step  in  an 
investigation. 


ELEMENTS,    MOLECULES,    AND    ATOMS.  127 

NEXT  WRITE  THE  REACTION.  —  Now  that  we  know  what 
substances  were  used  and  what  new  substances  were  made, 
the  next  step  is  to  use  formulas  and  signs  to  show  what 
happened. 

We  added  sodium  to  the  hydrochloric  acid  in  the  tube ; 
we  can  show  that  fact  by  writing  the  symbol  of  sodium, 
which  is  Na,  and  the  formula  of  the  acid,  which  is  H  Cl, 
with  the  sign  of  addition  between  them,  thus :  Na  +  H  Cl. 
We  know  by  the  taste,  and  by  the  explosion,  that  common 
salt  and  hydrogen  were  produced.  We  can  show  this  by 
writing  the  formula  of  common  salt,  or  sodium  chloride, 
Na  Cl,  and  the  symbol  of  hydrogen,  H,  with  the  sign  of 
addition  between  them,  thus:  NaCl  +  H.  We  know  that 
there  is  no  loss  nor  gain  of  matter  in  any  chemical  change. 
The  new  substances  must  contain  every  atom  of  the  old, 
and  no  others.  We  can  show  this  by  writing  the  old  sub- 
stances and  the  new,  with  the  sign  of  equality  between 
them.  Thus  we  have — • 

Na  +  H  Cl  =  Na  Cl  +  H 

We  read  this  reaction  in  this  way :  one  atom  of  sodium, 
with  one  molecule  of  hydrochloric  acid,  yield  one  mole- 
cule of  sodium  chloride,  and  one  atom  of  hydrogen.  This 
describes  the  chemical  change  which  took  place. 

Now  USE  ATOMIC  WEIGHTS.  —  This  chemical  expression 
may  be  changed  into  numbers  by  writing  the  atomic  weight 
of  each  element,  under  its  symbol,  wherever  that  symbol 
appears.  Thus  — 

Na  +  HC1  =  NaCl  -f  H 
23  +  (1  +  35.5)  =  (23  +  35.5)  +  1 
23  +  36.5  =  58.5  +  1 

If  we  had  to  make  a  quantity  of  common  salt  by  this 
process  this  last  equation  would  be  very  useful  because  it 
tells  us  just  how  much  of  the  substances  to  use.  We  may 


128  ELEMENTS,    MOLECULES,    AND    ATOMS. 

call  these  numbers  grains  or  grains  or  pounds,  or  any  other 
weights  we  please.  The  equation  shows  that  if  we  use  23 
grains  of  sodium  and  36,5  grams  of  hydrochloric  acid,  we 
can  get  just  58.5  grains  of  salt  and  1  gram  of  hydrogen. 
Knowing  this  it  is  easy  to  find  how  much  of  the  constit- 
uents to  take  for  any  desired  quantity  whatever  of  the 
compound. 

FINALLY  SOLVE  A  PROBLEM.  —  How  much  sodium  would 
be  needed  to  make  100  g.  of  common  salt  by  reaction  with 
hydrochloric  acid  ? 

If  for  58.5  g.  of  salt  we  need  23  g.  of  sodium,  then  for 
100  g.  of  salt  we  should  need  fcy  x  23,  which  is  39.31  + . 

ANOTHER  EXAMPLE.  —  Let  us  study  the  decomposition  of 
mercuric  oxide  by  heat.  We  have  made  the  experiment 
already.  In  Ex.  5  it  was  found  that  mercury  and  oxygen 
were  the  products.  We  take  the  symbols  from  the  table, 
p.  118,  and  write  the  reaction  thus : 

Hg  O  =  Hg  +  O 

Read  this  equation  in  full.  Refer  to  the  table  of  ele- 
ments, p.  118,  for  the  atomic  weights,  and  put  them  under 
the  symbols.  What  does  this  new  equation  show  ? 

How  much  mercury  could  be  obtained  from  100  g.  of  the 
oxide  ?  And  how  much  oxygen  ? 


ACIDS,    BASES,    A1ST>    SALTS. 

Acids.  — We  have  already  made  use  of  several  substances 
called  acids.  We  now  set  out  to  discover  just  what  is 
meant  by  the  term  acid.  Let  us  examine  a  few  of  these 
substances  for  this  purpose. 

Ex.  77.  —  I  fill  a  bottle  two-thirds  full  of  water  and  add 
enough  solution  of  blue  litmus  to  color  it  distinctly.  I 
next  add  dilute  sulphuric  acid,  1  of  acid  to  10  of  water, 
drop  by  drop,  and  note  the  change  in  color. 

I  now  add  a  drop  or  two  of  the  same  acid  to  a  test-tube 
nearly  full  of  water,  and  touch  a  drop  of  this  dilute  solution 
to  my  tongue,  and  note  the  taste  of  the  acid. 

I  finally  pour  5  cc.  of  strong  sulphuric  acid  into  40  cc. 
of  water  in  a  bottle,  drop  into  it  a  clipping  of  sheet-zinc, 
and  cover  the  bottle  with  a  square  of  heavy  paper.  In  a 
few  moments  I  bring  a  lighted  match  to  the  mouth  of  the 
bottle,  lifting  the  cover  at  the  same  time,  and  note  the 
combustion  which  takes  place.  What  is  this  gas  which 
is  set  free  by  the  metal  ?  ft  I 

Ex.  78.  —  I  now  use  hydrochloric  acid  instead  of  sul- 
phuric, and  again  note  the 

Change  in  the  color  of  the  blue  litmus. 
Taste  of  the  acid. 
Action  with  zinc. 

Ex.  79.  —  I  next  try  acetic  acid,  and  use  magnesium 
instead  of  zinc.  I  put  10  cc.  of  the  acid  in  a  test-tube,  and 
drop  upon  it  a  short  piece  of  magnesium  ribbon.  Note 
whether  the  same  gas  is  given  off  as  in  the  other  cases. 
Note  also  the  taste  of  the  acid,  and  its  action  on  blue  litmus. 


130  ACIDS,    BASES,    AND    SALTS. 

Ex.  80.  —  I  repeat  the  experiment  with  acetic  acid,  but 
use  iron  instead  of  magnesium.  I  add  the  iron  in  the  form 
of  filings,  or  the  smallest  tacks,  and  gently  heat  the  liquid. 

Is  there  any  gas  set  free  ?     Is  it  hydrogen  ? 

Ex.  81.  — I  use  acetic  acid  again,  but  this  time  I  add 
small  clippings  of  zinc,  and  heat  the  acid.  Is  the  action 
the  same  as  before  ? 

We  find  that  sulphuric  acid,  hydrochloric  acid,  and  acetic 
acid  are  alike  in  three  things :  they  are  all  sour  to  the  taste, 
will  redden  blue  litmus,  and  yield  hydrogen  by  the  action 
of  a  metal.  There  are  many  other  substances  having  these 
same  characters.  All  such  are  called  acids. 

THE  CHIEF  CHARACTERISTIC.  —  The  following  table  shows 
the  composition  of  several  acids,  by  formulas: 

Nitric  acid   .     .    .    .    ....    •.,•"•     •    •  H  N  O3 

Sulphuric  acid ..'....  H2  S  O4 

Phosphoric  acid    .     .     .    ....;;.     .     .  H8PO4 

Hydrochloric  acid H  Cl 

Hydroiodic  acid     .     .     '.     .    •.    .     *'-.-.     .  HI 

Hydrobromic  acid H  Br 

and  a  glance  at  these  symbols  shows  that  hydrogen,  H,  is 
a  constituent  in  every  one.  Every  acid  contains  hydrogen. 

But  there  are  many  compounds  containing  hydrogen 
which  are  not  acids.  An  acid  is  a  compound  containing 
hydrogen,  which  may  be  driven  out  by  a  metal,  as  in  our 
experiments.  This  is  the  chief  character  of  an  acid. 

THE  TWO  CLASSES.  —  Look  at  the  two  sets  of  formulas 
in  the  table.  In  each  acid  of  the  first  set,  oxygen,  O,  is 
present;  it  is  not  to  be  found  in  those  of  the  second. 

Now  we  may  learn  from  this  that  there  are  two  classes 
of  acids.  One  class  contains  the  element  oxygen,  the  other 
does  not. 


ACIDS,    BASES,    AND    SALTS.  131 

% 

Salts.  —  When  in  Ex.  77  our  zinc  drove  the  hydrogen 
•out  of  sulphuric  acid,  zinc  sulphate  was  also  made. 
If  we  write  the  reaction  — 


it  shows  how  zinc  and  sulphuric  acid  may  yield  hydrogen 
and  zinc  sulphate. 

We  see  that  1  atom  of  the  metal,  Zn,  takes  the  place  of 
2  atoms  of  hydrogen,  H2,  in  the  molecule  of  acid,  so  that 
instead  of  H2  S  04  we  have  Zn  S  04  . 

We  should  be  careful  to  notice  that  the  metal  puts  itself 
in  the  place  of  the  hydrogen  of  the  acid  to  form  the  new 
molecule. 

The  action  is  the  same  when  zinc  acts  on  other  acids 
instead  of  sulphuric.  The  zinc  drives  hydrogen  out  and 
puts  itself  in  the  place  of  it. 

Many  other  metals  have  the  same  power  to  act  upon 
acids.  Not  every  metal  can  do  this  to  every  acid  (Ex.  81), 
but  the  power  to  put  itself  in  the  place  of  hydrogen  in 
acids  is  very  common  among  the  metals. 

The  new  compounds,  formed  by  this  action  of  the  metals, 
are  called  salts.  When  sodium  and  hydrochloric  acid  are 
used,  the  new  compound,  as  we  have  seen,  is  common  salt  ; 
you  have  only  to  evaporate  the  liquid  to  get  the  familiar 
white  solid.  Every  acid  would  yield  a  different  kind  of 
salt  with  sodium.  Each  different  metal  also  yields  a 
different  salt  with  every  acid  on  which  it  acts. 

DEFINITION.  —  A  salt  is  a  com^pound  formed  by  putting  a 
metal  in  the  place  of  hydrogen  in  an  acid. 

Hydroxides  --  Some  metals  act  on  water  very  much 
as  the  metals  act  on  acids,  but  the  new  compounds  will  be 
of  a  quite  different  character.  Thus  : 

Ex.  82.  —  I  fill  a  bottle  half  full  of  water;  add  just 
enough  litmus  to  color  it  distinctly  ;  change  its  color  to  red 


132  ACIDS,    BASES,    AND   SALTS. 

by  stirring  it  with  a  rod  moistened  with  an  acid,  and  then 
drop  upon  its  surface  a  bit  of  sodium.  Note  the  change 
in  color,  and  prove  that  hydrogen  is  set  free. 

Ex.  83.  —  I  repeat  the  experiment,  but  use  25  cc.  of 
water  without  the  litmus.  When  the  sodium  is  gone,  I 
examine  the  liquid  in  three  ways: 

1.  I  moisten  the  end  of  a  rod  with  the  liquid,  touch  my 
tongue  with  it,  and  note  the  taste. 

2.  I  try  its  action  on  blue  litmus-water.     I  then  try  it  on 
red  litmus-water  in  this  way:    I  take  a  little  water   in   a 
tube,  blue  it  with  litmus,  and  then  redden  it  with  a  rod 
moistened  with  acid.     To  this  I  add  a  few  drops  of  the 
liquid,  and  note  the  change  in  color. 

3.  I  put  the  rest  of  the  liquid  in  a  porcelain  dish  and 
evaporate  it  to  dry  ness,  using  a  small  flame   toward  the 
end  of  the  operation,  and  note  the  appearance  of  the  solid 
left  behind. 

THE  FACTS.  —  The  sodium  decomposes  the  water,  and 
the  two  new  substances  are  hydrogen  gas,  and  a  white 
solid  which  is  very  "alkaline"  to  the  taste,  and  able  to 
restore  the  blue  color  to  reddened  litmus. 

We  may  write  the  reaction  in  the  usual  way: 

Na      +      H20  NaHO  +          H 

Sodium        Water        Sodium  hydroxide         Hydrogen 

and  this  shows  that  1  atom  of  the  metal,  Na,  takes  the 
place  of  1  atom  of  the  hydrogen,  H,  in  the  molecule  of 
water,  and  makes  a  new  molecule  of  what  is  called  sodium 
hydroxide,  Na  H  O.  This  sodium  hydroxide  is  the  white 
substance  left  behind  in  the  dish. 

It  is  named  for  the  elements  in  it  —  sodium,  hydro- 
gen, and  oxygen.  The  last  two  names  are  combined  in 
hydroxide,  and  so  we  get  the  name  sodium  hydroxide. 

In  like  manner  we  have  potassium  hydroxide,  K  H  0, 
and  ammonium  hydroxide,  Am  HO. 


ACIDS,    BASES,    AND    SALTS.  133 

Ex.  84.  —  I  half  fill  two  bottles  with  litmus-water  red- 
dened by  acid,  and  then  to  one  I  add  drops  of  potassium 
hydroxide  (caustic  potash)  solution  to  the  other  drops  of 
ammonium  hydroxide  (ammonia). 

Note  the  change  in  the  color  of  each. 

Carefully  learn  the  taste  of  each. 

THE  FACTS.  —  These  three  hydroxides  are  alike,  very 
alkaline  in  taste,  and  alike  able  to  restore  the  blue  of  red- 
dened litmus.  They  restore  the  blue  color  by  decomposing 
the  acid  which  reddened  it.  In  this  way  they  neutralize 
the  acids.  This  is  their  chief  characteristic. 

It  has  been  found  by  experiment,  that  nearly  all  metals 
have  compounds  of  this  kind.  The  hydroxides  are  a  very 
large  class  indeed. 

DEFINITION.  —  A  hydroxide  is  a  compound  of  a  metal 
with  hydrogen  and  oxygen,  which  will  neutralize  an  acid. 

OTHER  NAMES.  —  These  substances  are  also  called  hy- 
drates ;  instead  of  sodium  hydroxide  we  may  say  sodium 
hydrate.  They  are  also  called  bases.. 

Reaction  of  Bases  and  Acids.  —  But  how  does  a  base 
or  hydroxide  neutralize  an  acid  ?  Take  the  sodium  hy- 
droxide and  hydrochloric  acid  for  example. 

Ex.  85.  —  I  put  15  cc.  of  hydrochloric  acid  into  a  bottle 
and  drop  into  it  a  small  bit  of  litmus-paper,1  which  in- 
stantly becomes  red.  I  next  add  a  solution  of  sodium 
hydroxide  little  by  little,  shaking  or  stirring  the  liquid 
well  after  each  addition.  I  watch  the  color  of  the  litmus- 
paper  :  it  will  after  a  while  show  signs  of  turning  blue. 
I  then  add  the  hydroxide,  a  drop  at  a  time,  until  after  the 
last  drop  the  paper  remains  blue.  By  this  sign  I  know 
that  the  acid  is  neutralized. 

1  Litmus-paper  is  made  by  soaking  filter-paper  in  a  strong  solu- 
tion of  litmus  in  water  and  then  drying  it;  the  paper  has  a  deep  blue 
color. 


134  ACIDS,    BASES,   AND   SALTS. 

I  next  search  for  the  product  of  the  action.  I  put  tL<; 
liquid  into  a  porcelain  dish  and  evaporate  it  down  care- 
fully until  dry.  Let  it  cool,  and  then  examine  the  residue. 
Note  its  color  and  its  taste.  By  its  taste  we  know  what 
this  new  substance  is. 

We  find  that  common  salt  (Na  Cl)  is  one  product  of  the 
action  of  these  two  liquids.  By  writing  the  reaction,  we 
may  discover  that  there  should  be  another.  For  we  must 
have  new  substances  enough  to  contain  all  the  atoms  in  the 
old  ones.  Thus,  if  we  write  — 

HC1    +     NaHO    =    NaCl    +     HHOorH2O 
acid  base  salt  water 

we  see  that  water  must  be  a  product  of  the  action.  In 
this  case  the  acid  and  the  base  neutralize  each  other  by 
forming  a  salt  and  water. 

In  other  cases  the  action  is  the  same.  It  is  a  fact  that 
when  an  acid  arid  a  base  act  upon  each  other  the  result  is 
to  produce  a  salt  and  water.  There  are  few  exceptions 
(p.  95)  to  these  important  facts,  viz. : 

When  a  metal  acts  on  an  acid  a  salt  and  hydrogen  are 
produced.  When  a  base  acts  on  an  acid  a  salt  and  water 
are  produced. 

Neutral  Compounds.  —  Water  is  a  good  example  of 
bodies  which  are  neither  acids  nor  bases  nor  salts.  It 
will  not  change  the  color  of  litmus  either  to  red  or  blue. 
It  is  not  sour  to  the  taste  like  the  acids,  nor  caustic  like 
the  bases,  nor  is  it  made  by  putting  a  metal  in  the  place 
of  hydrogen  in  the  acids,  as  the  salts  are.  There  are  a 
great  many  other  compounds  like  water  in  these  respects. 
Bodies  which  will  not  change  the  color  of  either  blue  or  red 
litmus  are  called  neutral  bodies. 


ACIDS,    BASES,    AND    SALTS.  135 


CHEMICAL    NAMES. 

The  names  of  chemical  compounds  are  not  invented 
to  simply  suit  the  fancy  of  the  chemist ;  they  are  made 
by  certain  rules,  and  are  meant  to  show  the  composition  of 
the  substances  to  ivhich  they  are  given. 

The  Names  of  Acids Sulphuric  acid  is  made  up  of 

sulphur,  oxygen,  and  hydrogen;  its  name  is  so  made  that 
the  presence  of  these  three  things  is  shown. 

The  presence  of  sulphur  is  shown  by  using  the  name 
of  that  element.  The  presence  of  oxygen  is  shown  by 
the  ending  ic.  The  presence  of  hydrogen  is  shown  by  the 
word  acid,  because  all  acids  are  known  to  contain  this 
element. 

Sulphurous  acid  is  another  compound  of  these  same 
elements,  sulphur,  oxygen,  and  hydrogen.  Sulphur  is 
shown  by  its  own  name  as  before.  Oxygen  is  shown  by 
the  ending  ous.  Hydrogen  is  shown  by  the  word  acid  as 
before. 

It  will  be  seen  that  sulphuric  acid  and  sulphurous  acid 
are  made  of  the  same  elements.  The  first  contains  a  larger 
proportion  of  oxygen  than  the  other,  and  this  is  their  only 
difference  in  composition.  Now  ic  is  used  in  the  name  of 
the  one  that  contains  the  larger  proportion  of  oxygen,  and 
ous  in  the  name  of  the  other. 

In  the  same  way  we  have  two  acids  of  phosphorus : 
they  are  called  phosphoric  acid  and  phosphor  us  acid.  The 
first  contains  a  larger  proportion  of  oxygen  than  the  last. 
This  fact  is  shown  by  using  the  ending  ic  in  the  name  of 
the  first,  and  ous  in  the  name  of  the  last. 

In  some  cases  more  than  two  acids  are  made  of  the  same 
elements.  Prefixes  are  then  used  in  addition  to  the  end- 
ings ic  and  ous.  These  prefixes  are  hypo  and  per.  There 
is,  for  example,  the  hyposulphurous  acid.  It  contains  a 


136  ACIDS,    BASES,    AND    SALTS. 

less  proportion  of  oxygen  than  the  sulphurous  acid,  and 
this  is  shown  by  the  prefix  hypo.  The  prefix  per  means 
a  larger  proportion  of  oxygen.  There  is,  for  example, 
the  perchloric  acid.  It  contains  a  larger  proportion  of 
oxygen  than  the  chloric  acid:  this  is  shown  by  the  pre- 
fix per. 

The  Names  of  Salts.  —  The  name  of  a  salt  is  intended 
to  show  the  names,  of  the  metal  and  the  acid,  by  which  the 
salt  is  supposed  to  be  made.  If  sodium  act  on  sulphuric 
acid,  hydrogen  is  liberated  and  a  salt  is  at  the  same  time 
formed ;  this  salt  is  called  sodium  sulphate.  It  is  easy  to 
see  that  this  name  suggests  tho  name  of  the  acid  and  also 
of  the  metal.  When  sulphuric  acid  is  used  the  salt  which 
is  made  is  called  a  sulphate,  no  matter  what  metal  is 
employed. 

But  sulphurous  acid  yields  a  class  of  salts  which  are 
called  sulphites.  Notice  the  difference: 

Sulphuric  acid  yields  sulphates. 
Sulphurous  acid  yields  sulphites. 

The  same  difference  is  found  in  other  cases.  A  salt 
formed  by  chloric  acid  is  called  a  chlorate;  but  one  formed 
by  chlorous  acid  is  called  a  chlorite.  Nitric  acid  yields 
nitrates,  but  nitrous  acid  yields  nitrites. 

The  rule  is  this:  if  the  name  of  the  acid  ends  in  ic, 
the  names  of  its  salts  shall  end  in  ate;  but  if  the  name 
of  the  acid  ends  in  ous,  the  names  of  its  salts  shall  end 
in  ite. 

The  Names  of  Bases —  All  bases  are  made  up  of 
hydrogen,  oxygen,  and  a  metal,  and  their  names  show  this 
fact.  The  word  hydroxide  suggests  hydrogen  and  oxygen, 
and  hydroxide  is  the  name  of  this  whole  family  of  com- 
pounds. Each  individual  member  of  this  family  is  dis- 
tinguished by  the  name  of  the  metal  which  is  in  it. 


ACIDS,    BASES,    AND    SALTS.  137 

The  following  examples  will  make  this  method  clear. 
See  how  the  names  of  the  elements  suggest  the  name  of 
the  base  which  they  form,  and  how  the  name  of  the  base 
also  suggests  the  names  of  the  elements  of  which  it  is 

made. 

Sodium,  hydrogen,  oxygen,  form  the  Sodium  hydroxide. 
Potassium,      "  "  "        "     Potassium  hydroxide. 

Calcium,         "  «  «       «     Calcium  hydroxide. 

Iron,  "  "  "        «     Ferric  hydroxide. 

Iron,  -  «  «  "  Ferrous  hydroxide. 

There  are  in  many  cases  two  hydroxides  of  the  same 
metal,  and  the  endings  w  and  oiis  are  used  to  distinguish 
them.  The  names  of  the  iron  hydroxides  illustrate  this : 

Ferric  hydroxide    .     .'    . '  :    ^    .     .     Fe2(HO)6 
Ferrous  hydroxide     .    S  ...    .    .    Fe  (Hit)), 


CHLORINE  AND  THE  CHLORIDES. 

MORE  than  a  hundred  years  ago — it  was  in  1774 — the 
Swedish  chemist  Scheele  was  studying  the  action  of  hy- 
drochloric acid  on  a  black  powder  known  as  the  "black 
oxide  of  manganese."  To  his  surprise  a  heavy  greenish 
gas  was  produced.  Sir  Humphry  Davy  afterward  called 
this  gas  chlorine. 

Chlorine  is  a  very  suffocating  substance,  and  in  all  experi- 
ments with  it  we  must  be  careful  to  not  breathe  it.  When 
we  make  the  gas,  and  when  we  use  it,  there  must  be  the 
utmost  care  to  have  our  apparatus  air-tight,  and  to  prevent 
the  escape  of  this  noxious  gas. 

The  following  arrangement  of  our  gas-making  apparatus 
will  enable  chlorine  to  show  several  of  its  properties  with- 
out escaping  to  poison  the  atmosphere  of  the  room. 

Preparation  of  Chlorine.  —  We  will  adopt  the  original 
method,  and  make  the  gas  by  the  action  of  "black  oxide 

of  manganese" 
on  hydrochloric 
acid. 

Ex.  86.  —  In- 
to a  I  put  50  cc. 
water,  and  close 
the  flask  tightly 
with  its  stop- 
per. By  means 
of  a  piece  of 
small  wire  I 
hang  a  strip  of 
moist  blue  litmus-paper  to  the  stopper  of  I,  and  press  it 
down  into  the  flask. 


CHLORINE    AND    THE    CHLORIDES.  139 

I  fix  a  piece  of  "  gold  leaf  "  (Dutch  metal)  in  the  same 
way,  and  enclose  it  in  c.  I  fill  the  bulb  of  a  drying-tube 
loosely  with  cotton,  and  then  fill  the  wide  part  of  the 
tube  with  dry  slaked  lime  and  cork  it  tightly. 

I  then  join  all  these  parts,  as  shown  in  the  cut,  by  means 
of  rubber  tubing, — the  side-neck  with  the  long  glass  tube 
of  a,  the  short  tube  of  a  with  the  long  tube  of  b,  the 
short  tube  of  b  with  the  long  tube  of  c,  and  the  short  tube 
of  c  with  that  of  the  drying-tube,  the  small  end  of  which 
I  place  in  a  bottle,  d. 

Finally,  to  make  the  chlorine  I  put  25  g.  of  manganese 
dioxide,  Mn02,  into  the  side-neck  flask,  pour  in  upon  it 
100  cc.  strong  hydrochloric  acid,  press  home  the  solid 
rubber  stopper,  and  apply  a  small  flame  of  the  Bunsen. 
The  heat  must  be  gentle.  The  chlorine  will  slowly  drive 
the  air  over  from  flask  to  flask,  and  out  at  d;  but  if  the 
joints  are  as  tight  as  they  may  be,  no  chlorine  will  escape 
into  the  room. 

The  chlorine  soon  fills  the  side-neck  flask,  as  may  be 
seen  by  its  color,  and  then  bubbles  through  the  water  in 
a,  and  passes  slowly  on  toward  d. 

What  is  the  action  of  Cl  and  H2O,  shown  in  flask  a  ? 
What  is  the  effect  of  Cl  on  the  color  of  litmus,  shown  in  b? 
What  is  the  effect  of  Cl  on  Dutch  metal,  shown  in  c  f 
Why  are  there  no  bubbles  of  Cl  in  the  bottle  d  f 

THE  FACTS.  —  The  chlorine  comes  from  the  hydrochloric 
acid.  The  reaction  may  be  written  as  follows: 

Mn02        +        4HC1          =        MnCl2     +     2H2O  +  2C1 
Manganese  dioxide     Hydrochloric  acid     Manganese  chloride     Water      Chlorine 

Chlorine  is  a  greenish-yellow  gas,  whose  odor  is  pungent, 
and  suffocating  in  the  highest  degree.  Cold  water  dis- 
solves about  two  and  one-half  times  its  own  bulk  of  chlo- 
rine, and  then  has  the  same  color  as  the  gas  itself.  This 


140  CHLORINE   AND    THE    CHLORIDES. 

chlorine-water  may  be  used  instead  of  the  gas  for  many 
purposes ;  it  will  cause  the  same  chemical  actions.  We  see 
also  (flask  b)  that  chlorine  destroys  the  color  of  litmus, 
and  (flask  c)  that  it  combines  with  "  gold  leaf,"  and  that 
it  is  greedily  absorbed  by  the  lime  in  the  "  drying-tube." 

The  actions  of  chlorine  on  colors  and  on  the  metals  are 
important.  Let  us  study  them  further. 

Bleaching Chlorine  destroys  the  color  of  litmus  (b). 

Will  it  also  bleach  other  colors  ? 

Ex.  87.  —  I  fill  a  test-tube  half-full  of  water,  and  color 
it  with  black  writing-ink.  I  slip  the  rubber  tubes  off 
from  the  glass  tubes  of  flask  a,  and  then,  carefully  invert- 
ing the  flask  over  the  mouth  of  the  test-tube,  as  in  Fig.  57 
I  let  a  few  drops  of  chlorine-water  run  into  the  black  liquid. 

Ex.  88.  —  I  use  cochineal,  or  an  aniline  dye,  or  the  petal 
of  a  flower,  or  a  piece  of  calico  cloth,  instead  of  the  inky 
water  in  the  last  experiment. 

Ex.  89.  —  I  take  a  piece  of  paper  covered  with  writing  in 
red  ink,  and  a  piece  of  newspaper  covered  with  printing, 
and  moisten  both  with  the  chlorine-water. 

Is  the  color  discharged  in  both  cases  ? 

What  is  the  coloring  matter  of  printers'  ink? 

THE  FACTS.  —  This  power  of  chlorine  to  destroy  color- 
ing matters  is  made  use  of  on  a  large  scale  in  the  art  of 
bleaching.  All  colors  which  are  made  from  vegetable  or 
animal  substances  will  be  removed  by  chlorine  in  the 
presence  of  water :  dry  chlorine  does  not  bleach.  Nor  are 
mineral  colors  (carbon  of  printers'  ink)  disturbed  by  it. 
The  bleaching  of  linen  and  cotton  goods  and  paper  is  done 
by  the  use  of  chlorine. 

Chlorine  also  destroys  bad  odors,  and  it  is  much  used  in 
hospitals  and  elsewhere  for  this  purpose.  It  is  the  most 
powerful  disinfectant. 


CHLORINE    AND    THE    CHLORIDES.  141 

Chlorine  destroys  colors  and  odors,  by  taking  hydrogen 
away  from  them.  In  some  cases  the  color  or  the  odor 
gives  up  its  hydrogen  directly  to  the  chlorine,  but  in 
others  it  is  water  which  gives  up  its  hydrogen  to  the 
chlorine,  and  then  the  oxygen  which  is  set  free  attacks 
the  substance  of  the  color  or  the  odor  and  decomposes  it. 

BLEACHING  POWDER.  —  Chlorine  is  absorbed  quite  greedily 
by  slaked  lime.  The  product  is  called  bleaching  powder,  and 
this,  instead  of  chlorine-water,  or  the  gas  itself,  is  used  in 
the  arts. 

Ex.  90.  —  I  remove  a  part  of  the  lime  from  the  drying- 
tube,  Ex.  86,  to  a  dish  and  cover  it  with  water.  After 
stirring  it  well,  I  pour  it  on  a  filter,  and  catch  the  filtrate 
in  a  test-tube.  I  then  add  a  little  of  this  clear  solution  to 
some  inky  water  or  litmus  solution  in  another  tube. 

By  passing  chlorine-gas  over  dry  lime  in  large  chambers, 
instead  of  in  a  tube,  immense  quantities  of  this  powder 
are  made,  to  be  used  as  a  bleaching  agent  and  disinfectant. 

The  Chlorides Chlorine  readily  combines  with  the 

metals  and  changes  them  into  chlorides.  This  action  took 
place  in  flask  c  (Ex.  86).  The  leaf  of  "  Dutch  metal "  is 
said  to  be  made  of  zinc  and  copper,  and  if  so,  the  white 
residue  is  made  up  of  zinc  chloride  and  copper  chloride. 
Let  us  search  for  the  copper  chloride. 

But  we  should  first  examine  some  copper  chloride  itself, 
so  that  we  may  be  able  to  identify  it. 

Ex.  91.  —  I  put  a  little  of  a  known  specimen  of  copper 
chloride  into  a  test-tube  and  add  a  little  water.  It  easily 
dissolves. 

What  is  the  color  of  the  strong  solution  ? 
What  is  the  color  if  more  and   more  water  be  added  ? 
What   happens  if  a  piece  of  clean  iron  is  left  in  the 
solution  ? 


142  CHLORINE    AND    THE    CHLORIDES 

I  next  add  to  some  solution  in  another  tube  a  little 
ammonia,  and  then  add  more,  and  more,  until  the  blue 
precipitate  made  at  first  is  dissolved  to  a  clear,  fine  blue 
liquid. 

A  compound  of  copper  may  be  known  by  the  green  or 
blue  color  of  its  solution,  by  the  metallic  copper  set  free  by 
iron,  and  by  the  action  of  ammonia. 

Ex.  92.  —  I  now  carefully  take  the  stopper  and  tubes 
from  the  flask  c ;  the  white  residue  of  the  metal  is  lifted 
out  with  them.  I  carefully  wash  this  residue  into  a  porce- 
lain dish  with  as  little  water  as  will  remove  it.  I  look  for 
the  color,  and  if  I  find  none  I  evaporate  the  solution  down 
to  a  small  bulk.  Finally,  I  insert  a  bright  clean  needle  or 
knife-blade  and  leave  it  a  few  minutes. 

Compare  these  results  with  those  in  Ex.  91,  and  decide 
whether  the  chlorine  produced  copper  chloride  in  the 
flask  c,  in  Ex.  86. 

CHLORIDES  BY  CHLORINE  WATER.  —  Metals  are  changed 
to  chlorides,  not  only  by  chlorine  gas,  but  also  by  chlorine 
water.  Thus : 

Ex.  93.  —  I  put  a  leaf  of  "Dutch  metal,"  about  two  square 
inches,  into  a  test-tube  and  pour  upon  it  5  cc.  chlorine-water 
from  a,  and  shake  it  until  dissolved.  I  then  carefully 
slide  a  clean  iron  nail  down  into  the  solution. 

Does  the  color  of  the  solution  indicate  a  copper  com- 
pound ?  Does  the  action  of  the  iron  prove  its  presence  ? 

After  half  an  hour  take  out  the  iron,  and  put  in  a  fresh 
bright  piece.  If  the  action  is  over  no  copper  will  now  be 
deposited.  Keep  this  liquid  for  Ex.  97. 

CHLORIDES  BY  HYDROCHLORIC  ACID.  —  But  the  most 
usual  way  of  changing  metals  to  chlorides  is  by  means  of 
hydrochloric  acid.  Thus: 

Ex.  94-  — Into  5  cc.  strong  hydrochloric  acid  I  put  several 


CHLORINE    AND    THE    CHLORIDES.  143 

small  bits  of  iron,  such  as  small  tacks.  Hydrogen  escapes 
with  effervescence.  I  let  the  tube  stand  until  the  action  is 
over. 

Note  the  color  of  the  iron  chloride  now  in  solution. 

Get  the  solid  chloride  out,  by  evaporating  the  liquid. 

The  reaction  may  be  written  in  this  way : 

Fe      +      2  H  Cl      =      Fe  C12      +       2  H 

Iron  Acid  Ferrous  chloride       Hydrogen 

which  shows  that  an  atom  of  iron,  Fe,  takes  the  place 
of  two  atoms  of  hydrogen  in  the  acid,  and  makes  a  new 
molecule  of  ferrous  chloride,  setting  two  atoms  of  hydro- 
gen free.  Thus  the  iron  is  changed  into  a  chloride. 

Iron  has  a  stronger  attraction  for  chlorine  than  hydrogen 
has,  and  can  take  the  chlorine  away  from  the*  hydrogen  in 
the  acid.  This  is  also  true  of  many  other  metals  beside 
iron. 

CHLORIDES  BY  AQUA  REGIA.  —  When  strong  hydrochloric 
acid  is  mixed  with  nitric  acid,  they  decompose  each 
other;  chlorine  is  set  free,  but  stays  in  the  solution. 
Now  this  mixture  will  do  what  neither  of  the  acids  sepa- 
rately can  do :  it  will  dissolve  gold  and  platinum,  changing 
them  into  chlorides.  Gold  has  been  called  the  king  ot 
metals,  and  this  liquid  which  dissolves  it  is  called  aqua 
regia,  the  meaning  of  which  is  "  royal  water."  Aqua  regia 
is  the  most  powerful  of  all  agents  for  changing  metals  into 
their  chlorides.  For  example  : 

Ex.  95.  —  I  put  2  cc.  strong  hydrochloric  acid  into  a  test- 
tube  and  add  about  one-fourth  as  much  strong  nitric  acid. 
Into  this  I  drop  two  or  three  small  "tacks."  Chemical 
action  is  evident  at  once,  and  the  iron  slowly  wastes  away. 
The  liquid  changes  color  as  the  iron  chloride  increases, 
and  toward  the  end  orange  vapors  of  a  suffocating  odor 
may  appear.  Keep  this  liquid. 


144  CHLORINE   AND    THE    CHLORIDES. 

Two  Chlorides  of  one  Metal The  color  of  the  liquid 

containing  the  iron  chloride  made  by  aqua  regia  is  quite 
different  from  that  of  the  iron  chloride  made  by  hydro- 
chloric acid.  Let  us  try  to  find  the  reason. 

Ex.  96.  —  I  repeat  the  experiment  with  hydrochloric 
acid  (Ex.  94),  and  when  the  action  is  over  compare  the 
liquid  with  that  made  by  aqua  regia  in  Ex.  95. 

Note  the  difference  in  color. 

I  next  test  a  part  of  each  of  these  two  solutions  sepa- 
rately with  ammonia,  just  as  I  did  the  copper  solution  in 
Ex.  91. 

Note  the  great  difference  in  the  two  results. 

Do  the  two  solutions  contain  the  same  or  different  sub- 
stances ? 

THE  FACTS.  —  The  iron  chloride,  made  by  hydrochloric 
acid,  is  green,  while  that  made  by  aqua  regia  is  yellow. 
When  ammonia  is  added  they  behave  very  differently :  the 
first  gives  a  light  green  precipitate,  while  the  last  gives  one 
that  is  reddish-brown.  These  differences  lead  us  to  think 
that  there  must  be  two  different  chlorides  of  iron,  and 
this  is  true. 

The  green  chloride  is  FeCl2,  called  ferrous  chloride. 

The  yellow  chloride  is  Fe2Cl6,  called  ferric  chloride. 

In  the  names  of  the  two  chlorides  of  iron  the  endings  ic 
and  otts  show  the  two  proportions  of  chlorine,  ic  the  larger 
and  ous  the  smaller.  With  many  other  metals,  also, 
chlorine  forms  both  ic  and  ous  chlorides. 

Ex.  97.  —  When  the  iron,  in  Ex.  93,  took  the  copper  out 
of  the  copper  chloride,  what  else  occurred  ?  To  the  liquid 
kept  from  that  experiment  add  ammonia,  and  from  the 
color  of  the  result  decide 

Whether  it  contains  copper  chloride  or  iron  chloride. 

Whether  it  contains  ferrous  or  ferric  chloride. 


CHLORINE    AND    THE    CHLORIDES.  145 

You  can  then  understand  just  what  happened  in  Ex.  93. 
.For  if  the  ammonia  gives  the  green  precipitate,  then  fer- 
rous chloride  is  present,  and  the  iron  must  have  changed 
the  copper  chloride  into  it.  Thus : 

CuCl2     +      Fe     =     FeCl2        -f       Cu 

Copper  chloride         Iron         Ferrous  chloride         Copper 

Atoms  of  iron  took  the  place  of  atoms  of  copper,  and 
changed  the  copper  chloride  to  the  ferrous  chloride. 

Hydrogen  Chloride This  is  another  name  for  hydro- 
chloric acid,  —  one  of  the  strongest  and  most  useful  of  all 
acids.  It  is  made  on  a  large  scale  from  common  salt  by 
the  help  of  sulphuric  acid.  On  a  small  scale  we  may  pre- 
pare it  with  the  apparatus  used  for  chlorine,  leaving  out 
only  the  drying-tube,  as  shown  in  Fig.  59. 

Ex.  98.  —  I  put  50  cc.  strong  sulphuric  acid  in  a,  press 
its  stopper  home,  and  join  its  long  tube  with  the  side- 
neck.  I  leave  b 
empty  (it  should 
be  dry),  close 
it  with  the  stop- 
per and  join  to 

a.  I  put  a  strip 
of  moist  blue  lit- 
mus-paper   in    c, 
and  join  it  with 

b.  The  bottle  d 
contains     water, 
into    which    the 

tube    from    c   is  Fig  s3 

put  with  its  end  scarcely  more  than  covered.  Finally  I 
put  the  materials,  dry  salt,  5  g.,  and  strong  sulphuric  acid, 
10  cc.,  into  the  side-neck,  and  close  it  tightly.  The  reac- 
tion sets  in  at  once;  but  to  keep  it  up,  I  apply  a  very  gen- 


146  CHLORINE    AND    THE    CHLORIDES. 

tie  heat  so  that  bubbles  will  be  seen  in  a  a  little  faster 
than  one  can  count.  The  acid  in  a  is  used  to  absorb  mois- 
ture which  comes  over  with  the  gas  ;  the  gas  will  be  dried 
by  the  acid  if  it  does  not  come  over  too  fast. 

Note  the  action  of  the  hydrochloric  acid  on  litmus. 

Note  the  color  of  the  gas. 

What  is  the  effect  of  the  water  in  the  bottle  d? 

Ex.  99.  —  I  remove  the  cork  and  tubes  from  flask  b,  and 
then  invert  the  flask  with  its  mouth  in  a  vessel  of  water. 
The  water  quickly  rises  to  almost  fill  the  flask. 

How  can  you  account  for  this  result  ? 

THE  FACTS.  —  The  reaction  when  sodium  chloride,  Na  Cl, 
and  sulphuric  acid  H2  S  O4  ,  are  gently  heated  is  this  : 


NaCl  +  H2S04  =  HNaS04  + 

The  hydrochloric  acid,  H  Cl,  is  a  colorless  gas  which  in- 
stantly reddens  litmus  and  dissolves  with  great  freedom 
in  water.  The  so-called  hydrochloric  acid,  of  commerce  and 
the  laboratory,  is  a  solution  of  this  gas  in  water. 

Composition  of  Hydrochloric  Acid  by  Volume.  —  If 
hydrogen  and  chlorine  gases  are  mixed,  they  will  combine 
when  exposed  to  light,  and,  by  measuring  the  gases,  it  has 
been  found  that  it  takes  just  as  many  cubic  centimeters  of 
hydrogen  as  of  chlorine.  Pure  hydrochloric  acid  contains 

1  volume  of  hydrogen  and  1  volume  of  chlorine. 

But  now,  how  much  hydrochloric  acid  will  these  two 
volumes  of  its  elements  make  ?  It  has  been  found  that  if 
10  cc.  of  hydrogen  and  10  cc.  of  chlorine  are  used,  there 
will  be  just  20  cc.  of  the  hydrogen  chloride  made. 

One  volume  hydrogen  and  1  volume  chlorine  make  2  vol- 
umes hydrogen  chloride. 

Now  compare  this  fact  with  another  noted  under  the 


CHLORINE    AND    THE    CHLORIDES.  147 

composition  of  water,  p.  56,  and  still  another  noted  under 
the  composition  of  ammonia,  p.  90. 
We  see  that  in  the  case  of 

H  Cl,    2  volumes  of  the  elements  make  2  volumes  of  compound. 
H2O,  3        «          «  "  «      2 

H8N,  4        "          "  "  "      2 

Just  two  volumes  of  the  compound  gas  is  made  every 
time !  The  same  thing  is  found  true  of  other  compound 
gases  also.  Take  the  five  compounds  of  nitrogen  and  oxy- 
gen, for  example : 

2  volumes  N  and  1  volume    O  make  2  volumes  nitrous  oxide. 

1  volume    N    ';     1  volume    O      "      2         "        nitric  oxide. 

2  volumes  X    "     3  volumes  O      "      2         "         nitrous  anhydride. 

1  volume    N    "     2  volumes  O      "      2         "         nitrogen  peroxide. 

2  volumes  N    "     5  volumes  O      "      2        "        nitric  anhydride. 

These  are  the  results  of  experiments.  And  so,  whether 
we  have  two  volumes  of  the  constituents,  as  in  the  second, 
or  seven  volumes,  as  in  the  fifth,  there  are  just  two  volumes 
of  the  compound  made  when  they  combine.  If  we  put 
all  these  facts  into  one  statement,  we  have  this  law:  The 
volume  of  a  compound  gas  is  TWO,  whatever  may  be  the 
number  of  volumes  of  the  elements  in  it. 

Test  for  Chlorine  and  the  Chlorides Let  a  drop  of 

silver  nitrate  solution  be  added  to  a  solution  of  chlorine 
or  of  any  chloride,  and  a  white  cloud  or  precipitate  will  ap- 
pear. This  white  precipitate  is  silver  chloride.  It  will 
become  dark  colored  if  left  a  little  while  in  the  sunlight. 
Try  this  test  on  several  chlorides. 

THE    CHLORINE    GROUP. 

There  are  three  other  elements  which  are  so  much  like 
chlorine,  that  the  four  are  together  called  the  chlorine 
group.  They  behave  so  nearly  like  chlorine,  and  their 


148  CIILOKINE    AND    THE    CHLORIDES. 

uses  are  so  much  less  important,  that  we  need  not  stop 
long  with  them  in  our  study. 

Bromine A  little  more  than  half  a  century  after  the 

discovery  of  chlorine  —  it  was  in  the  year  1820  —  M. 
Balard,  a  French  chemist,  found  another  element,  with 
properties  much  like  those  of  chlorine.  Its  odor  was 
found  to  be  so  strong  that,  in  honor  of  this  characteristic 
the  element  was  called  bromine.  The  word  is  from  the 
Greek  word  fipaifioz  (bromos),  which  means  stench. 

Bromine  is  not  very  abundant,  but  it  does  exist  in  the 
waters  of  some  mineral  springs,  and  in  larger  quantities 
in  the  waters  of  the  sea.  It  is  always  found  in  combina- 
tion, and  its  compounds  are  called  bromides. 

Bromine  is  a  lif/uid,  but  a  very  gentle  heat  changes  it 
to  gas.  It  has  a  beautiful  dark-red  color. 

This  element  readily  combines  with  hydrogen  and  with 
metals;  in  this  respect  it  is  like  chlorine,  and  like  that 
element  it  is  able  to  remove  colors  and  to  destroy  bad 
odors. 

Iodine M.  Courtois  was  a  chemical  manufacturer  in 

Paris.  He  was  engaged  in  making  soda,  and  was  using 
the  ashes  of  sea-weeds  for  this  purpose.  A  dark-colored 
liquid  was  left  in  his  kettles,  and  attacked  the  metal  of 
which  they  were  made.  When  some  sulphuric  acid  was 
put  with  it,  this  liquid  gave  up  a  substance  which,  when 
heated,  changed  to  a  beautiful  violet-colored  vapor.  It 
proved  to  be  a  new  element,  and  it  was  called  iodine. 
This,  from  the  Greek  word  iwdqg  (iodas),  means  viof.et- 
colored. 

Iodine  is  a  constituent  of  sea-plants,  as  we  may  know 
from  the  story  of  its  discovery.  The  sea  contains  it  in 
small  quantities,  and  so  do  the  waters  of  some  mineral 
springs.  It  is  an  element  in  sponges,  and  in  oysters,  and 
in  some  fishes.  It  is  always  found  in  nature,  combined 
with  other  substances. 


CHLORINE   AND    THE   CHLORIDES.  149 

Iodine  is  a  solid.  A  gentle  heat  melts  it,  and  a  little 
higher  temperature  changes  it  into  its  beautiful  vapor. 

Water  dissolves  it,  but  a  single  grain  will  take  no  less 
than  7000  grains  of  water  to  dissolve  it.  How  small  this 
proportion  of  iodine,  and  yet  it  gives  to  the  whole  body 
of  the  water  a  brownish-yellow  color  !  Alcohol  will  •  dis- 
solve it  in  large  proportions.  This  solution  in  alcohol  is 
the  "tincture  of  iodine,"  used  in  medicine. 

Iodine  combines  with  hydrogen  and  with  many  metals. 
In  this  respect  it  is  much  like  chlorine  and  bromine.  Its 
compounds  are  called  iodides. 

Some  of  its  compounds  with  the  metals  are  remarkable 
for  their  very  brilliant  colors  (Ex.  13). 

But  there  is  one  effect  of  iodine  which  neither  chlorine 
nor  bromine  can  produce:  it  is  the  fine  blue  color  it  gives 
to  starch.  Thus  : 

Ex.  100.  —  I  boil  a  bit  of  starch  in  a  half  test-tubeful 
of  watert  and  after  it  has  become  cold  I  add  a  little  iodine- 
water,  made  by  vigorously  shaking  a  crystal  of  iodine  in 
water.  Note  the  blue  color  produced. 

Compounds  of  iodine  do  not  blue  the  starch ;  the  experi- 
ment may  be  made  with  potassium  iodide.  But  if  one  of 
these  can  be  decomposed  the  free  iodine  will  show  itself 
by  the  color ;  the  experiment  may  be  made  by  adding  drops 
of  nitric-acid  to  the  solution  of  potassium  iodide,  and  then 
adding  the  starch.  The  test  for  free  iodine  is  starch. 

The  physician   finds  iodine -very  useful   as  a  medicine. 

The  photographer  finds  it  very  valuable  in  the  art  of 
picture-making. 

The  element  itself  is  sometimes  used  in  medicine,  but 
its  compounds  are  more  generally  used  in  the  arts. 

Fluorine.  —  This  element  is  found  in  combination  with 
the  metals,  and  all  attempts  to  get  it  free  have  failed.  Its 
chemical  attractions  are  so  strong,  that  if  it  be  set  free  it 


150  CHLORINE    AND    THE    CHLORIDES. 

immediately  combines  with  something  else ;  even  with  the 
substance  of  the  vessel  in  which  the  work  is  done.  And 
yet  it  is  remarkable  that  this  is  the  only  element  which 
is  not  known  to  combine  with  oxygen.  Its  strongest 
affinities  are  for  hydrogen  and  the  metals.  We  cannot 
say  whether  fluorine  is  a  gas,  or  would  be  if  out  of 
combination,  as  chlorine  is.  It  is  supposed  that  it 
would  be,  because  it  is  a  much  lighter  substance  than 
chlorine.  It  is  only  nineteen  times  heavier,  while  chlo- 
rine is  35.5  times  heavier  than  an  equal  bulk  of  hydrogen. 

The  mineral  called  fluor  spar,  CaF2,  is  the  most  abund- 
ant compound  of  fluorine.  When  this  is  treated  with 
sulphuric  acid  the  fluorine  leaves  the  calcium,  Ca,  and 
combines  with  hydrogen.  This  gives  a  gas, — the  hydro- 
fluoric acid,  HF.  This  acid  gas  is  useful  in  the  art  of 
etching  glass;  for  wherever  it  touches  glass  the  fluorine 
leaves  the  hydrogen  to  unite  with  the  elements  of  the 
glass  instead. 

Hydrogen  Compounds.  —  Fluorine,  chlorine,  bromine, 
and  iodine  behave  toward  hydrogen  very  much  alike. 
Each  one  forms  a  single  compound  with  that  element,  and 
each  one  combines  with  the  hydrogen,  atom  for  atom. 
Their  names  and  formulas  plainly  show  this  fact.  Thus: 

Hydrochloric  acid II  Cl 

Hydrobromic  acid .     .  H  Br 

Hydroiodic  acid HI 

Hydrofluoric  acid    .    .»  ,-   *.,;  .w  ;»«...  HF 

This  is  a  very  interesting  fact,  for  there  is  no  other 
non-metal,  besides  these  four,  that  will  combine  with  hy- 
drogen atom  for  atom.  In  the  case  of  oxygen,  for  example, 
the  compound  is  water,  H20,  in  which  an  atom  of  oxy- 
gen takes  two  atoms  of  hydrogen.  An  atom  of  oxygen 
refuses,  absolutely,  to  ever  take  any  less  than  two  of 
hydrogen. 


CHLORINE    AND    THE    CHLOUWEX.  151 

General  Behavior.  —  These  four  elements  behave  very 
much  alike  in  other  respects.  This  is,  to  be  sure,  not  quite 
so  marked  in  the  case  of  fluorine  as  in  the  other  three, 
but  in  general  they  combine  witlrthe  same  elements  and  in 
the  same 'proportions.  And  they  are  able  to  do  the  same 
kinds  of  work ;  as,  for  instance,  chlorine  bleaches  colors ;  so 
does  bromine,  and  iodine  also,  when  in  solution. 

Chlorine  is  a  better  bleacher  than  bromine,  —  it  is  more 
powerful,  and  bromine  is  a  better  bleacher  than  iodine. 
But  they  are  all  bleachers. 

Atomic  Weights  and  Properties In  general  it  is 

true  in  other  cases,  as  well  as  in  bleaching,  that  the  chem- 
ical action  of  chlorine  is  more  vigorous  than  that  of 
bromine,  and  of  bromine  more  vigorous  than  that  of  iodine. 
In  fact,  bromine  will  drive  iodine  out  of  combination  and 
take  its  place,  and  chlorine  will  treat  bromine  in  the  same 
way.  Now  this  order  of  chemical  strength  is  just  the 
order  of  their  atomic  weights,  beginning  with  the  smallest. 
Thus : 

Atomic  weight  of  Cl    35.5,  with  most  vigorous  chemical  action. 
Atomic       "        "   Br   80        "     less  "  "  " 

Atomic       "        "   I    127        "     least         "  "  " 

Their  forms,  gaseous,  liquid,  and  solid,  are  in  the  same 
order ;  so  are  the  densities  of  these  elements.  In  fact,  the 
properties  of  these  elements  seem  to  depend,  in  some  way, 
on  their  atomic  weights. 

EXERCISES. 

1.    Study  the  actions  of  chlorides,  bromides,  and  iodides  on 

silver  nitrate. 

1.  Arrange  three  test-tubes,  one  with  a  little  solution 
of  sodium  chloride,  another  with  as  much  solution  of 
potassium  bromide,  and  another  with  as  much  solution  of 

O       0^  TBOi        ^^ 


152  CHLORINE    AND    THE    CHLORIDES. 

potassium  iodide.  Add  silver  nitrate  drop  by  drop,  shak- 
ing the  tube  vigorously  after  each  addition,  until  a  drop 
fails  to  make  a  precipitate.  Describe  the  precipitates. 
Note  the  effect  of  shaking  them.  Look  carefully  for  some 
difference  in  their  colors. 

Then  expose  the  tubes  to  sunlight,  or  for  some  time  to 
diffuse  light,  and  note  the  changes  which  occur  in  the 
colors. 

2.  Next  test  the  solubility  of  these  precipitates  in  am- 
monium hydrate.     To  do  this,  make  a  little  fresh  precipi- 
tate, and  keep  it  from  light  as  much  as  possible.     When 
the  precipitate  has  settled,  decant  the  liquid,  that  is,  pour 
it  away  carefully  so  as  to  leave  the  precipitate  in  the  tube. 
Then   pour   upon   it  ammonium   hydrate   gradually,   with 
shaking,  until  you  can  decide  whether  the  precipitate  dis- 
solves.    Do  they  all  dissolve?     Does   one   dissolve   more 
easily  than  another  ? 

3.  Write  a  brief  statement  of  all  the  facts  which  you 
have  discovered,  noting  particularly  the  points  of  difference 
among  the  three  compounds. 

2.    Study  the  action  of  chlorides,  bromides,  and  iodides  on 
starch. 

1.  Make  a  very  thin  starch-water,  by  boiling  a  minute 
piece   of   starch   in   considerable   water,   and   cooling    the 
liquid. 

2.  Dissolve  a  chloride,  a  bromide,  and  an  iodide,  each  in 
water. 

3.  To  a  part  of  each  solution  add  a  few  drops  of  nitric 
acid,  and  afterward  add  a  little  of  the  starch-water.     There 
should  be  a  difference  in  color  produced  ;  note  it  carefully. 

To  another  part  of  each  solution  add  a  little  of  the  cold 
starch-water,  without  the  nitric  acid.  By  this  means  you 
can  decide  whether  nitric  acid  is  necessary  to  bring  out  the 
colors  observed  before. 


CHLORINE    AND    THE    CHLORIDES.  153 

4-  Add  the  starch-water  to  hot  solutions  instead  of  cold 
ones,  and  let  them  become  cold.  By  this  means  yon  will 
learn  the  effect  of  heat. 

5.  Write  a  brief  statement  of  all  the  facts  which  you 
have  discoverd. 

Chlorine,  bromine,  and  iodine  behave  so  very  much  alike, 
that  it  is  not  always  easy  to  distinguish  their  compounds 
one  from  another.  And  then,  too,  there  is  another  class  of 
compounds  called  cyanides,  which  might  be  mistaken  for 
some  of  these.  Still  the  "  silver-nitrate,"  and  the  "  starch 
test,"  will  help  one  to  identify  these  three  classes  of  com- 
pounds. In  the  case  of  the  nitrate  test,  the  pure  precipi- 
tates differ  a  little  in  color,  and  more  in  solubility  in 
ammonia,  —  the  chloride  being  easily  soluble,  the  bromide 
much  less  so,  and  the  iodide  almost  not  at  all.  In  the 
starch  test,  nitric  acid  must  be  used  to  decompose  the  com- 
pounds, because  it  is  only  the  free  iodine  which  gives  the 
blue,  and  the  free  bromine  which  gives  the  brown  color. 

3.  Take  a  few  substances  from  the  teacher,  or  a  friend  who 
knows  what  they  are,  and  see  if  you  can  decide  whether 
each  is  a  chloride,  bromide,  or  an  iodide. 


SULPHUR    AND    ITS    COMPOUNDS. 

Native  Sulphur Sulphur  seems  to  have  been  known 

and  used  in  the  most  ancient  days  of  which  we  have  any 
account.  The  element  itself,  and  its  compounds  also,  are 
very  abundant  in  the  earth.  The  element  itself,  or  native 
sulphur,  is  found  in  the  neighborhood  of  volcanos,  or  where 
these  fire-mountains  have  been  active  in  time  past.  Large 
quantities  are  taken  from  mines  in  Sicily ;  in  fact,  a  great 
part  of  the  sulphur  in  commerce  comes  from  this  source. 

Native  Sulphides.  —  Sulphur  is  found  combined  with 
metals  in  the  rocks  and  soils  almost  everywhere.  These 
compounds  are  called  sulphides. 

The  sulphide  of  iron  is  a  good  example.  It  is  a  brassy- 
looking  substance,  very  common  in  many  rocks.  It  is  often 
found  in  the  form  of  little  cubes,  as  perfect  as  if  they 
had  been  chiselled  by  an  artist.  Sometimes  it  is  found  in 
the  form  of  thin,  shining,  yellow  scales.  It  has  been 
called  "fool's  gold,"  because  the  ignorant  have  been  de- 
ceived by  its  color.  It  is  iron  disulphide,  FeS2,  and  is 
commonly  called  iron  pyrites. 

The  sulphides  are  the  substances  from  which  the  useful 
metals  are  often  obtained.  Lead,  for  example,  is  taken 
from  the  mineral  called  galena,  but  galena  is  the  lead  sul- 
phide, Pb  S.  Silver,  copper,  and  zinc  are  also  among  the 
useful  metals,  found  in  the  rocks  in  combination  with 
sulphur. 

Preparation  of  Sulphur.  —  In  its  native  state,  as  found 
in  the  mines  of  Sicily,  sulphur  is  not  combined  with  any- 
thing, but  yet  it  is  very  far  from  being  ready  for  the  mar- 
ket. It  is  not  in  comlination,  but  it  is  mixed  with  a  great 
deal  of  earthy  impurities  from  which  it  must  be  separated. 

154 


SULPHUR    AND    ITS    COMPOUNDS.  155 

This  is  easily  done,  because  sulphur  is  easily  changed  into 
vapor  by  heat,  while  the  earthy  impurities  are  not.  Let 
the  mixture  be  heated,  then,  and  the  sulphur-vapor  will 
pass  away  and  leave  the  impurities  behind.  The  vapor, 
being  cooled  again,  is  sulphur,  which  is  very  much  more 
free  from  earthy  matter  than  before. 

It  is  heated  a  second  time  to  remove  the  impurities 
which  the  first  process  did  not.  This  time  the  vapor  is 
run  into  a  large  chamber,  and  it  is  condensed  upon  the 
cold  walls  in  very  fine  powder.  This  powder  is  the  "  flowers 
of  sulphur  "  which  is  so  common. 

When  the  chamber  is  smaller,  its  walls  become  too  hot  to 
collect  the  powder,  which  then  melts,  and  the  liquid  runs 
down  upon  the  floor.  It  runs  into  channels  in  the  floor 
which  lead  it  out  of  the  chamber  into  moulds.  In  this  way 
the  familiar  sticks  of  "  roll  brimstone  "  are  made  for  the 
market. 

Effects  of  Heat  on  Sulphur.  Ex.  101.  —  I  reduce  a 
piece  of  brimstone  to  coarse  powder  and  half  fill  a  test-tube 
with  it.  I  hold  the  tube  in  the  hot  air  above  the  lamp-flame, 
and  thus  keep  it  from  contact  with  too  strong  a  heat,  but 
lower  it  until  I  find  the  heat  intense  enough  to  melt  the 
sulphur.  The  liquid  should  not  be  darkened,  but  be  yellow 
and  limpid. 

Ex.  102.  —  I  place  the  tube  with  the  limpid  yellow  liquid 
where  it  will  not  be  shaken,  and  watch  the  liquid  while  it 
slowly  cools. 

In  what  form  does  the  sulphur  solidify  ? 

Ex.  103.  —  I  now  carefully  re-melt  the  sulphur,  and  then 
make  the  yellow  liquid  a  little  hotter, — only  a  little. 

Note  the  change  in  color. 

I  continue  to  heat  the  liquid  gradually  and  incline  the 
tube  from  time  to  time,  and  observe  that  the  color  deepens 
and  the  sulphur  grows  viscid  until  it  refuses  to  flow  at  all. 


136  SULPHUR    AND    ITS    COMPOUNDS. 

I  then  heat  it  still  more,  and  notice  that  the  half-solid 
sulphur  re-melts. 

I  continue  to  apply  heat  to  find  out  whether  the  sulphur 
can  be  boiled,  and  what  is  the  color  of  the  vapor. 

I  then  pour  the  liquid  in  a  small  stream  into  a  vessel  of 
cold  water,  and  examine  the  sulphur  after  this  sudden 
cooling. 

THE  FACTS.  —  Sulphur  at  ordinary  temperature  is  a 
bright  yellow  solid,  but  when  heated  a  little  hotter  than 
boiling  water  (114.5°  C.)  it  melts  to  a  limpid  yellow  liquid. 
Some  care  is  required  to  preserve  this  yellow  color,  since 
it  easily  changes  if  the  heat  be  much  greater. 

At  a  higher  temperature,  about  132°,  the  sulphur  begins 
to  grow  viscid  as  well  as  dark  colored.  Darker  and  thicker 
it  becomes  as  it  gets  hotter,  until,  at  about  230°,  it  is  almost 
black,  and  is  so  very  viscid  that  it  will  not  flow  from  the 
vessel  even  if  turned  bottom  upward.  Make  the  hot  sul- 
phur still  hotter,  and  the  dark-colored,  almost  solid  sub- 
stance grows  less  viscid  again ;  it  will  flow  in  the  vessel 
very  much  like  thick  syrup. 

At  a  higher  temperature,  about  450°,  the  sulphur  boils. 
The  hot  vapor  is  colorless,  but  if  cooled  a  little  it  is  con- 
densed and  becomes  yellow. 

PLASTIC  SULPHUR.  —  If  melted  sulphur,  just  below  its 
boiling-point,  be  poured  into  cold  water,  it  cools  into  a  sub- 
stance which  looks  like  India-rubber.  If  we  handle  it,  we 
find  that  it  is  like  India-rubber  in  other  things  besides  its 
color:  it  is  tough  and  elastic.  This  unusual  form  of  sul- 
phur is  called  plastic  sutyhiu:  It  will  not  stay  in  this 
condition,  but  gradually  it  will  become  again  yellow  and 
brittle  as  at  first.  This  plastic  sulphur  is  almost  as  unlike 
the  common  form  as  if  it  were  another  element.  In  these 
two  forms  we  find  a  good  example  of  allotropism,  p.  39. 

CRYSTALS  OF  SULPHUR.  —  If  melted  sulphur,  limpid  and 


SULPHUR    AND    ITS    COMPOUNDS.  157 

yellow,  be  allowed  to  cool  slowly  (Ex.  102),  fine  needle- 
shaped  crystals  will  be  seen  to  shoot  out  from  the  walls  of 
the  vessel.  They  will  increase  in  number  and  size,  until 
finally,  when  cold,  the  solid  mass  of  sulphur  will  be  made 
up  of  these  slender  prisms  interlaced  and  crowded  together. 

Crystals  of  sulphur  are  also  found  in  nature,  but  their 
shape  (rhombic  octohedra)  is  quite  unlike  that  of  the  arti- 
ficial crystals  obtained  by  fusion.  In  these  two  forms  of 
sulphur  we  have  a  good  example  of  dimorphism)  —  the  prop- 
erty in  virtue  of  which  a  substance  may  crystallize  in  two 
distinct  forms.  Sulphur  is  called  a  dimorphorus  element, 
because  it  crystallizes  in  two  shapes. 

Artificial  Sulphides.  —  A  sulphide  of  copper  can  be 
made  as  follows  : 

Ex.  104-  —  I  prepare  a  small  coil  of  fine  copper  wire, 
No.  30,  by  winding  the  wire  around  a  small  lead-pencil  or 
glass  tube.  I  put  a  few  fragments  of  sulphur  into  a  tube, 
and  then  insert  the  coil  and  heat  the  sulphur  to  boiling. 
Watch  for  any  sign  of  chemical  action,  and  notice  that, 
once  well  started,  it  will  run  to  the  upper  end  of  the  coil 
without  the  further  aid  of  the  flame. 

Compare  the  substance  of  the  coil  now  with  the  copper 
and  the  sulphur  which  were  used. 

Ex.  105.  —  The  experiment  may  be  made  by  mixing  4  g. 
flowers  of  sulphur  with  8  g.  of  fine  copper-filings,  and  heat- 
ing this  mixture  in  a  test-tube. 

THE  FACTS.  —  When  copper  and  sulphur  are  heated  to- 
gether they  unite  and  form  a  compound  which  is  grayish- 
black,  and  brittle.  The  lamp-flame  brings  them  to  the 
right  temperature,  when  at  once  the  action  sets  in.  -  A 
vivid  red  glow  begins,  and  goes  quickly  to  the  end  of  the 
coil  or  mixture.  This  glow  is  not  due  to  the  lamp-flame, 
because  it  goes  on  even  if  the  flame  is  taken  away.  The 


158  SULPHUR    AND    ITS    COMPOUN])S. 

additional  heat  to  make  the  glow  must  l>e  caused  by  the 
chemical  action  itself.     Thus  : 

Materials.  Products. 

Cu  +  S  CuS  +  heat 

Many  other  metals,  like  copper,  will  become  sulphides 
when  heated  with  sulphur.  If  a  white-hot  rod  of  iron  is 
used  to  stir  melted  sulphur,  the  iron  will  become  iron 
sulphide,  and  if  zinc  and  sulphur  are  properly  heated,  zinc 
sulphide  is  obtained. 

These  artificial  sulphides  are  not  always  the  same  as 
the  native  sulphides  of  the  same  metals.  This  artificial 
sulphide  of  iron,  for  example,  is  very  different  from  the 
native  pyrites.  It  is  Fe  S,  while  the  native  sulphide  is 
FeS2;  the  first  is  the  ferrous  sulphide,  while  the  second 
is  the  ferric  sulphide. 

Hydrogen  Sulphide.  —  The  ferrous  sulphide  is  very 
easily  decomposed  by  acids. 

Ex.  106.  —  I  put  a  piece  of  ferrous  sulphide,1  not  larger 
than  a  grain  of  wheat,  into  a  test-tube,  and  pour  upon  it 
1  cc.  dilute  hydrochloric  acid  (half  water). 

Notice  the  effervescence :  what  does  it  show  ? 

Notice  the  odor  in  the  tube. 

Notice  the  color  of  the  liquid  when  the  action  is  over. 

Add  ammonia  to  the  liquid  and  compare  with  Ex.  96. 

THE  FACTS. — By  the  action  of  the  acid  and  sulphide  a 
gas  is  set  free  with  effervescence,  and  its  bad  odor  — 
like  that  which  arises  from  the  putrefaction  of  certain 
things,  such  as  eggs  —  proves  this  gas  to  be  hydrogen  sul- 
phide. The  ammonia  test  suggests  the  presence  of  ferrous 
chloride  in  the  liquid.  Hence  the  reaction  is  as  follows: 

FeS  +  2HC1  =  FeCl2  +  H2S 

1  This  substance  is  sold  in  the  form  of  "sticks,"  which  is  very 
much  better  than  the  powder  or  the  granular  form. 


SULPHUR    AND    ITS    COMPOUNDS.  159 

The  H2S  is  the  hydrogen  sulphide:  it  is  also  called 
sulphuretted  hydrogen. 

This  gas  is  found  in  the  waters  of  "sulphur  springs." 
All  the  sulphur  which  such  springs  contain  is  in  the  form 
of  this  gas.  They  owe  their  nauseous  taste  and  odor,  and 
their  medicinal  value,  to  hydrogen  sulphide  dissolved  in 
their  waters. 

This  gas  is  a  powerful  agent  for  changing  the  metals 
into  sulphides;  no  other  substance  is  so  valuable  to  the 
chemist  for  this  purpose. 

Preparation  and  Properties.  —  In  order  to  study  the 
behavior  of  this  gas  without  being  annoyed  by  its  escape 
into  the  room,  we  may  employ  our  usual  form  of  gas  ap- 
paratus. 

Ex.  107.  —  Put  40  cc.  water  into  a,  Fig.  60,  to  cover 
the  lower  end  of  the  long  tube.  Add  a  cubic  centimeter 
of  solution  of  lead 
acetate,  and  a  drop 
or  two  of  hydrochlo- 
ric acid  to  40  cc. 
of  water,  and  put 
the  mixture  into  b. 
Into  c  put  40  cc. 
water  containing 
some  arsenious  ox- 
ide solution,  and 
several  drops  of 
acid,  and  into  d  put 
20  cc.  dilute  ammo-  rig' 60' 

nium  hydrate  (half  water).   Connect  the  parts   of  the  ap- 
paratus, and  be  sure  that  the  joints  are  tight. 

Finally,  put  10  g.  ferrous  sulphide,  in  small  pieces,  into 
the  side-neck  flask,  and  pour  upon  it  30  cc.  of  dilute  hydro- 
chloric acid  (half  water),  and  stopper  the  flask  at  once. 


100  SULPHUR    A XI)    ITS    COMFWXDS. 

The  air  will  be  gradually  driven  out  of  the  flasks,  and 
then  the  H2S  will  begin  to  show  its  presence  by  its  ac- 
tion on  the  liquids  through  which  it  passes. 

Note  its  color  as  seen  above  the  liquids. 

Note  the  results  of  its  action  on  the  lead  compound. 

Note  its  different  action  on  the  "arsenic." 

Note  the  effect  of  the  ammonium  hydrate. 

Let  the  action  go  on  until  the  effervescence  stops.  Then 
take  flask  a  out  of  the  series,  and  transfer  a  little  of  its 
water  to  tubes  for  the  following  purposes. 

What  is  the  odor  of  this  water? 

What  is  the  effect  of  adding  to  it  drops  of  H  Cl  and 
then  of  lead  acetate  ? 

What  is  the  effect  of  adding  to  it  drops  of  H  Cl  and 
then  of  arsenic  solution  ? 

Does  the  water  have  the  same  effects  as  the  gas  itself  ? 

THE  FACTS.  —  Sulphuretted  hydrogen  is  a  colorless  gas 
which  is  dissolved  by  water  quite  freely  (a).  The  gas  in 
solution  behaves  just  like  the  gas  alone,  readily  changing 
metallic  compounds  into  sulphides. 

This  gas  is  also  very  soluble  in  ammonium  hydroxide 
(e),  but  in  this  case  the  solution  is  not  a  simple  one,  as 
in  water :  there  is  chemical  action  between  the  two  sub- 
stances, and  the  result  is  ammonium  sulphide. 

Use  in  Analysis.  —  It  is  easy  to  see  (flasks  b  and  c)  that, 
if  one  has  a  solution  which  contains  either  lead  or  arsenic, 
without  knowing  which,  sulphuretted  hydrogen  will  help 
him  to  decide,  for  lead  sulphide  is  black  while  arsenious 
sulphide  is  yellow.  So  this  gas  is  often  used  to  identify 
the  metals  in  the  work  of  analysis. 

But  it  is  still  more  often  used  by  the  chemist  to  separate 
two  or  more  metals  whose  compounds  are  mixed.  An 
example  will  show  how  this  may  be  done. 


SULPHUR    AND    ITS    COMPOUNDS.  161 

Ex.  108.  — I  mix  1  cc.  strong  solution  of  copper  chloride 
and  1  cc.  strong  solution  of  zinc  chloride,  and  then  add 
10  cc.  H2  S  solution  freshly  made  (Ex.  107).  I  let  the  black 
precipitate  settle  and  then  add  drops  more  of  the  H2S 
solution,  to  see  whether  more  precipitate  forms.  I  must 
add  the  hydrogen  sulphide  as  long  as  it  will  make  the  pre- 
cipitate, but  when  it  refuses  to  do  more  I  filter  the  whole 
into  a  clean  tube  or  bottle.  I  now  have  the  black  pre- 
cipitate in  the  funnel,  and  the  clear  liquid  in  the  vessel 
below. 

This  liquid  should  contain  all  the  zinc  and  none  of  the 
copper.  Test  it  by  adding  a  few  drops  of  ammonium 
hydroxide :  the  presence  of  zinc  and  absence  of  copper 
is  shown  by  a  white  precipitate,  without  the  blue  which 
copper  would  yield. 

The  black  precipitate  should  contain  all  the  copper  and 
none  of  the  zinc.  Test  it  by  putting  a  little  in  a  tube 
and  warming  it  with  a  few  drops  of  nitric  acid  to  dissolve 
it,  then  adding  a  little  water,  and  finally  adding  am- 
monium hydroxide.  The  copper  will  be  shown  by  the 
familiar  blue  color. 

THE    SULPHUR    GROUP. 

There  are  three  other  elements  whose  chemical  actions 
are  very  much  like  those  of  sulphur.  These  are  selenium, 
tellurium,  and  oxygen. 

Selenium.  —  Selenium  is  a  rare  element,  which  is  found 
in  combination  with  some  metals,  such  as  copper  and  iron. 
These  compounds  are  called  selenides.  The  element  is  a 
solid.  It  burns  in  the  air  with  a  reddish-blue  flame,  and 
an  odor  peculiarly  offensive,  even  worse  than  that  of  burn- 
ing sulphur.  It  is  a  conductor  of  electricity,  if  it  be  first 
melted  and  then  slowly  cooled,  but  not  a  conductor  if 
cooled  quickly.  Its  symbol  is  Se. 


162  SULPHUR    AND    ITS    COMPOUNDS. 

Tellurium.  —  Tellurium  is  even  more  rarely  found  than 
selenium.  The  element  is  bluish-white,  and  has  a  fine 
luster.  Like  sulphur  and  selenium,  it  is  found  in  the  earth 
combined  with  metals,  such  as  gold,  silver,  and  lead.  Its 
symbol  is  Te. 

Their  Hydrogen  Compounds.  —  Sulphur,  selenium,  and 
tellurium  unite  with  hydrogen,  and  in  the  same  propor- 
tions. Each  one  combines  with  the  hydrogen,  not  atom  for 
atom,  but  one  atom  for  two.  In  this  respect  they  are  like 
oxygen.  Their  names  and  formulas  plainly  show  this  fact. 
Thus : 

Hydrogen  oxide H2  O 

Hydrogen  sulphide H2  S 

Hydrogen  selenide H2  Se 

Hydrogen  telluride H2  Te 

Now  these  four  are  the  only  non-metals  which  combine 
with  hydrogen  in  this  way  —  one  atom  with  two.  But 
these  do  so  always. 

General  Behavior These  four  elements  act  very 

much  alike  in  other  respects.  They  combine  with  the  same 
things  and  in  the  same  proportions.  This  is  not  quite  so 
well  marked  in  the  case  of  oxygen,  which  stands  a  little 
apart  from  the  rest ;  but  still  the  likeness  is  very  strong, 
and  these  four  form  a  well-marked  natural  group. 

Atomic  Weights  and  Properties.  —  The  order  of  the 
atomic  weights  in  this  group  is  as  follows: 

O  S  Se  Te 

16  32  79  125 

This  is  also  the  order  of  their  specific  gravities.  When 
equal  volumes  are  weighed,  O  is  found  to  be  the  lightest, 
and  S,  Se,  and  Te  are  heavier  in  this  order.  It  is  also  the 
order  of  their  melting-points ;  oxygen  melts  at  a  very  low 
temperature,  S  melts  at  about  114°  C.,  Se  at  217°,  and  Te 


SULPHUR    AND    ITS    COMPOUNDS.  163 

at  500°.  It  is  also  the  order  of  their  energy  in  chemical 
action,  that  of  O  being  greatest  and  of  Te  least.  The 
gradually  varying  properties  of  this  set  of  elements  stand 
in  the  order  of  their  atomic  weights.  This  is  the  second 
case  of  this  kind  (see  p.  151).  Are  there  other  instances  ? 
We  shall  see. 

SULPHUROUS    OXIDE    AND    ACID. 

Burning  of  Sulphur.  —  We  have  found  (Ex.  8)  that 
sulphur  will  burn  freely  in  oxygen,  with  a  rich  blue  flame, 
and  that  the  product  will  dissolve  in  water,  which  will  then 
redden  blue  litmus.  We  have  also  found  (Ex.  43),  that 
sulphur  will  readily  burn  in  air.  The  product  of  combus- 
tion, in  both  cases,  is  sulphur  dioxide,  SO2,  which  is  more 
commonly  called  sulphurous  oxide. 

Preparation  of  SO2 — This  oxide  is  easily  made  by 
heating  sulphuric  acid  with  copper. 

Ex.  109.  —  I  put  10  g.  of  copper,  in  small  pieces,  such  as 
clippings  of  sheet-copper  or  wire,  into  the  side-neck  flask 


Fig.  61. 


of  the  gas  apparatus  (Fig.  61),  and  pour  upon  it  about  20  cc. 
of  strong  sulphuric  acid. 


104  svLPJin;  .i.v/>  ITS 

I  put  15  cc.  of  water  in  a,  15  cc.  of  sulphuric  acid  in  b, 
and  50  cc.  of  water  in  e,  and  I  then  join  the  series  «,  t>,  r, 
rf,  e,  as  usual,  the  long  tube  of  each  with  the  short  tube  of 
the  one  in  front  of  it,  and  a  with  the  side-neck. 

I  now  heat  the  side-neck  flask  with  a  small  flame  until 
effervescence  begins,  and  afterwards  just  enough  to  keep 
the  action  going.  The  liquid  will  froth  over  if  the  heat  is 
too  strong.  A  little  white  vapor  of  sulphuric  acid  goes  over 
into  a,  but  the  true  appearance  of  the  oxide  should  be  seen 
in  b,  and  in  the  other  flasks. 

What  is  the  color  of  sulphurous  oxide  ? 

Can  you  decide  whether  the  gas  is  absorbed  by  H20  in  e? 

To  discover  the  Properties  of  Sulphurous  Oxide 

When  the  action  is  over  I  at  once  take  all  the  flasks  apart, 
and  then  examine  the  gas  they  contain. 

Ex.  110.  —  I  thrust  a  strip  of  moist  blue  litmus-paper 
into  a  and  leave  it  hanging,  held  by  the  stopper  which  I 
press  in  beside  it.  I  suspend  a  strip  of  dry  blue  litmus- 
paper  in  the  same  way  in  b.  Note  any  difference  in  the 
action  of  the  moist  and  dry  gas. 

Ex.  111.  —  I  lower  the  flame  of  a  small  taper,  or  of  a 
splinter  of  wood,  into  the  gas  in  a,  and  decide  — 
What  is  the  effect  of  sulphurous  oxide  on  flre  ? 

Ex.  112.  —  If  I  boil  a  few  small  chips  of  logwood  in 
water  I  get  a  rich  wine-colored  solution.  I  do  this,  and 
then,  taking  a  test-tube  half  full  of  the  colored  water,  I  add 
some  of  the  water  from  flask  e. 

What  is  the  effect  of  S  O2  on  this  color  ? 

Ex.  113.  —  I  transfer  a  little  of  the  water  from  e  to  a, 
dish  or  tube,  and  test  it  to  learn  — 
Whether  it  has  the  odor  of  the  gas. 
Whether  it  is  an  acid. 


SULPHUR    AND    ITS    COMPOUNDS.  165 

Ex.  114-  —  At  this  point  I  take  the  tubes  from  c  and  d, 
and,  closing  the  flasks  with  solid  corks,  I  stand  them  aside 
for  use  at  another  time  (Exs.  117,  118).  I  pour  the  brown 
liquid  carefully  out  of  the  side-neck  flask,  leaving  the  almost 
black  sediment  behind,  and  then  put  in  about  50  cc.  of 
water,  shake  it  well,  and  filter  the  whole  into  a  dish  or 
bottle.  I  keep  this  deep-blue  liquid  also  for  use  at  a  future 
time  (Ex.  121).  Pour  the  liquids  from  «,  b,  e  into  the 
waste,  take  out  their  stoppers  and  stand  the  flasks  mouth 
down  in  water,  and  leave  them  until  the  noxious  gas  is 
absorbed. 

THE  FACTS.  —  Sulphurous  oxide  is  a  gas  with  no  color, 
but  possessing  an  odor  of  the  most  pungent  and  suffocat- 
ing kind,  —  the  odor  of  a  burning  "Lucifer  match."  The 
dvy  gas  will  not  redden  blue  litmus,  but  when  moist  it 
will  do  so  readily.  It  dissolves  in  water  very  freely,  and 
this  solution  is  an  acid.  It  will  also  bleach  the  color  of 
logwood  and  many  other  substances ;  this  the  dry  gas  will 
not  do. 

Sulphurous  Acid The  dry  gas,  and  its  solution,  act 

quite  differently  on  litmus,  and  also  on  coloring  matter, 
and  by  this  we  know  that  the  gas  is  not  simjrly  dissolved 
in  the  water,  as  in  the  case  of  chlorine,  and  of  hydrogen 
sulphide,  but  that  a  chemical  change  has  taken  place. 

The  fact  is,  that  the  gas  unites  with  water ; 

SO2         4-        H2O         =         H2SO8 

Sulphurous  oxide  Water  Sulphurous  acid 

and  while  the  oxide  itself  is  not  an  acid,  its  compound 
with  the  elements  of  water  is. 

There  are  many  other  oxides  like  the  sulphurous  oxide 
in  this  respect, — they  will  combine  with  the  elements  of 
water,  and  thus  form  acids.  All  such  oxides  are  called 
anhydrides. 


166  SULPHUR    AXD    ITS    COMPOUNDS. 

This  one  is  called  the  sulphurous  anhydride,  because  it 
unites  with  the  elements  of  water,  and  becomes  sulphur- 
ous acid. 

Bleaching.  —  The  power  of  moist  sulphurous  oxide  to  re- 
move colors  makes  this  substance  very  valuable  for  bleach- 
ing. Articles  of  straw,  silk,  and  wool  are  bleached  on  a 
large  scale,  by  first  moistening  them  and  then  hanging 
them  hi  chambers  in  which  sulphur  has  been  burned. 
The  sulphurous  oxide  does  not  act  on  the  color  itself,  but 
it  decomposes  water  and  sets  free  a  part  of  the  hydrogen. 
This  hydrogen  then  acts  on  the  colors,  and  changes  them  to 
colorless  compounds.  Unfortunately  these  colorless  com- 
pounds will  be  decomposed  on  exposure  to  air  and  light, 
and  then  the  color  returns. 

Sulphurous  oxide  will  not  burn,  nor  will  it  allow  the 
combustion  of  anything  else ;  the  fumes  of  burning  sulphur 
will  extinguish  fire. 

SULPHURIC    ACID    AND    THE    SULPHATES. 

Some  Properties  of  the  Acid If  we  examine  a 

specimen  of  strong  sulphuric  acid,  which  can  be  found 
in  every  laboratory,  we  find  that  it  is  a  heavy  oily-acting 
liquid.  For  this  reason  it  is  called  oil  of  vitriol.  If  we 
taste  it  —  which  we  must  not  do  without  first  diluting  it 
with  a  large  quantity  of  water  —  we  find  it  to  be  sourer 
than  the  strongest  vinegar.  If  we  touch  it,  we  find  our 
fingers  smarting  almost  as  if  it  had  been  fire.  If  we  drop 
it  upon  our  garments,  we  find  them  turning  red  wherever 
touched  by  it,  and  that,  some  days  after,  the  red  spots 
crumble  into  holes. 

When  mixed  with  water  the  strong  acid  unites  with  it 
at  once,  and  the  mixture  is  heated  as  if  by  fire  (Ex.  14). 
This  violent  attraction  between  the  acid  and  water  throws 
light  upon  some  well-known  facts,  thus : 


SULPHUR    AND   ITS    COMPOUNDS.  167 

Ex.  115.  —  I  put  2  or  3  cc.  of  oil  of  vitriol  into  a  test- 
tube  and  place  in  it  the  end  of  a  clean  pine  stick.  After 
a  few  minutes  I  find  the  wood  to  be  as  black  as  if  it  had 
been  scorched.  Indeed,  the  wood  is  changed  very  much 
as  it  would  be  by  fire.  For  by  fire  a  black  coal  is  left, 
while  the  other  elements  are  driven  away. 

What  are  the  elements  in  wood?     See  p.  101. 
Which  one  of  these  is  left  behind  by  the  acid  ? 
Then  which  ones  are  taken  out  by  it  ? 
Why  does  the  acid  extract  these  ? 

One  of  our  earliest  experiments  showed  the  singular 
effects  of  this  acid  on  sugar  (Ex.  2),  and  now  you  can 
no  doubt  find  in  the  composition  of  the  sugar,  and  this 
property  of  the  acid,  a  good  explanation  of  that  action. 
Do  so. 

Some  uses  of  Sulphuric  Acid — The  chemist  very 
often  needs  the  gases,  with  which  he  works,  to  be  per- 
fectly dry ;  he  remembers  this  strong  attraction  between 
sulphuric  acid  and  the  elements  of  water,  and  makes  his 
gas  bubble  through  some  of  the  acid.  It  comes  off  dry. 

Sulphuric  acid  is  used  in  making  a  great  many  materials 
used  in  the  arts,  such  as  soap,  soda,  alum,  and  other  kinds 
of  chemicals. 

It  is  used  also  in  coloring  cloth,  in  printing  calico,  and 
then,  at  other  times,  it  assists  in  the  work  of  bleaching. 

Many  thousands  of  tons  a  week,  of  sulphuric  acid,  are 
made  and  distributed  over  the  world  to  be  used  for  these 
and  other  purposes  in  the  arts.  The  manufacture  of  sul- 
phuric acid  is  one  of  the  most  important  industries. 

Test  for  Sulphuric  Acid.  —  If,  to  any  liquid  which 
contains  this  acid,  a  solution  of  barium  chloride  is  added, 
a  white  precipitate  will  be  made,  which  cannot  be  dis- 
solved by  water  or  acids.  Thus: 


168  SULPHUR    A XI)    ITS    COMPOUNDS. 

Ex.  116.  — To  half  a  test-tube  full  of  water  I  add  a  drop 
of  H2S04,  and  a  half  cubic  centimeter  of  H  Cl,  and  then  I 
add  a  solution  of  barium  chloride  (Ba  C12)  drop  by  drop. 
The  white  precipitate  (BaS04)  which  comes,  in  spite  of 
the  hydrochloric  acid,  shows  the  presence  of  H2SO4.  Try 
this  test  on  a  solution  of  any  of  the  sulphates. 

The  Manufacture  of  Sulphuric  Acid.  —  The  process 
is  founded  on  a  few  simple  facts,  which  we  can  easily 
demonstrate,  and  for  this  purpose  we  have  the  flasks  full 
of  S  02  kept  over  from  Ex.  114.  The  S  O2  may  be  made  by 
burning  sulphur  in  oxygen  (Ex.  8 ),  or  in  air  (Ex.  43),  but 
we  may  use  that  already  made  in  the  other  way.  The 
question  is  now,  How  can  this  sulphurous  oxide  be  changed 
into  sulphuric  acid  ? 

Ex.  111.  —  I  wet  a  shaving  or  splinter  of  wood  with 
strong  nitric  acid  and  thrust  it  into  the  sulphurous  ox- 
ide of  flask  d  (Ex.  114),  and  leave  it  there  awhile. 

Notice  the  colored  fumes  which  are  produced. 

What  is  the  meaning  of  these  ?     See  Ex.  62. 

It  may  be  well  to  insert  the  splinter,  wet  with  nitric 
acid,  a  second  time.  But  finally  I  take  it  out,  pour  10  cc. 
of  water  into  the  flask,  and  shake  it  well,  to  dissolve  as 
much  as  possible  of  the  contents,  then  pour  it  into  a  test- 
tube  and  label  ^it  d. 

Ex.  118.  —  And  now  to  find  out  whether  the  sulphur- 
ous oxide  has  been  changed  by  the  nitric  acid  I  will  dis- 
solve the  gas,  which  still  remains  in  flask  c  (Ex.  114)  in 
10  cc.  water,  and  then  compare  this  solution  with  the 
other,  labelled  d,  in  this  way :  I  first  add  -a  half  cubic 
centimeter  of  hydrochloric  acid,  and  then  add  drops  of 
barium  chloride,  to  each  of  my  two  solutions. 

Note  the  difference  in  results. 

What  substance  did  the  solution  d  contain  ? 


SULPHUR    AND    ITS    COMPOUNDS.  169 

The  Changes.  —  When  we  bring  sulphurous  oxide  and 
nitric  acid  together  yellowish-red  fumes  appear  (Ex.  117), 
and  by  these  colored  fumes  we  know  that  the  nitric  acid  is 
being  decomposed.  Sulphurous  oxide  in  water  will  yield 
no  white  precipitate  with  a  mixture  of  hydrochloric  acid 
and  barium  chloride,  but  after  this  action  of  nitric  acid  the 
solution  will  (Ex.  118).  By  this  we  know  that  the  S  O2 
has  been  so  changed  that  its  solution  in  water  is  sulphuric 
acid. 

If  now  we  could  only  take  the  water  out  of  the  sul- 
phuric acid  again,  we  could  see  what  the  S  O2  had  been 
changed  into.  Unfortunately  we  cannot  do  this  by  experi- 
ment, but,  fortunately,  we  can  represent  the  process  by 
formulas,  as,  in  arithmetic  or  algebra,  we  often  show  by 
signs,  the  work  which  we  do  not  actually  do.  From  sul- 
phuric acid,  H2SO4,  let  us  subtract  water,  H20. 

H2S04-H20  =  S(>3 

It  must  have  been  S  O3  which,  when  dissolved  in  water, 
gave  the  sulphuric  acid  which  we  found  in  e/,  and  hence 
the  SO2  must  have  been  changed  into  SO3  by  the  nitric 
acid. 

This  S03  is  called  sulphuric  oxide.  It  is  also  called  sul- 
phuric anhydride,  because  it  combines  with  water  to  make 
sulphuric  acid. 

THE  FACTS.  —  What,  then,  are  the  facts  which  we  have 
found  ?  They  are  as  follows  : 

1.  The  burning  of  sulphur  yields  sulphurous  oxide. 

2.  ^Sulphurous   oxide  will  take  oxygen  from  nitric  acid 
and  become  sulphuric  oxide. 

3.  Sulphuric  oxide  dissolves  in  water  and  becomes  sul- 
phuric acid. 

APPLICATION  OF  THESE  FACTS. — These  are  the  facts 
on  which  the  manufacture  of  sulphuric  acid  is  founded. 


170  SULPHUR   AND    ITS    COMPOUNDS. 

In  the  actual  process  there  are  a  few  others,  but  for  the 
full  details  you  may  refer  to  some  larger  chemistry.1 

The  acid  is  made  in  immense  lead-lined  chambers.  Such 
a  chamber  may  be  100  feet  long,  20  feet  wide,  and  almost 
as  high  as  it  is  wide.  Sulphurous  oxide  goes  over  into 
this  chamber  from  a  furnace  where  sulphur,  or  iron 
pyrites,  is  burning.  Xitric  acid,  made  on  the  spot,  also 
enters  the  chamber,  while  jets  of  steam  are  blown  in,  and 
a  full  supply  of  air  is  kept  up. 

The  acid,  which  is  made  in  this  chamber,  is  too  dilute 
for  use,  and  it  is  made  stronger  by  evaporation  in  lead 
pans,  and  then  still  stronger  by  evaporation  in  vessels  of 
glass  or  platinum.  These  must  be  used  instead  of  lead 
pans  toward  the  last,  because  the  strong  acid  will  corrode 
the  lead. 

The  Sulphates.  —  The  salts  made  by  sulphuric  acid  are 
called  sutyhates.  We  may  study  these  as  follows : 

Ex.  119. — To  MAKE  ZINC  SULPHATE.  —  I  dilute  some 
strong  sulphuric  acid  by  pouring  5  cc.  of  it  into  40  cc.  of 
water  contained  in  a  wide-mouth  bottle,  and  drop  into 
this  small  pieces  of  zinc.  I  let  the  action  go  on  until  the 
acid  is  used  up,  adding  more  zinc  if  necessary.  When  the 
effervescence  has  almost  stopped,  with  zinc  still  left  in 
the  bottle,  I  filter  the  liquid  to  get  rid  of  the  black  flakes 
which  come  from  impure  zinc.  I  next  evaporate  the  liquid 
to  one-half  its  bulk,  and  then  let  it  cool.  While  it  cools, 
crystals  will  be  seen  forming  in  the  liquid.  These  crystals 
are  zinc  sulphate. 

Ex.  120.  —  To  MAKE  FERROUS  SULPHATE.  —  I  make 
some  dilute  sulphuric  acid,  as  in  the  last  experiment,  and 

1  In  Hoscoe  and  Schorlemmer,  Vol.  I.  pp.  319-338,  is  a  full 
account.  In  Cooley's  Text-Book  of  Chemistry,  p.  108,  the  reactions 
are  given  briefly. 


SULPHUR    AND    ITS    COMPOUNDS.  171 

drop  into  it  small  iron  nails,  such  as  small  "tacks."  I 
cover  the  bottle  with  a  plate  of  glass  or  a  square  of  heavy 
paper,  and,  after  the  action  has  gone  on  for  some  time, 
I  lift  the  cover,  and  at  the  same  time  bring  a  match-flame 
to  the  mouth  of  the  bottle  and  discover 

What  gas  is  set  free  by  the  action? 

When  the  action  is  over  I  filter  the  liquid,  and  then 
evaporate  it  down  to  half  its  bulk,  and  let  it  cool.  If  the 
evaporation  has  gone  far  enough,  crystals  will  appear. 
These  crystals  are  ferrous  sulphate. 

Ex.  121.  —  To  MAKE  COPPER  SULPHATE.  —  For  this 
purpose  the  strong  acid  is  needed  instead  of  the  dilute, 
and  heat  must  be  used.  This  work  was  done  in  experi- 
ment 109,  and  if  the  deep  blue  liquid  has  been  kept  (Ex. 
114),  we  need  not  now  repeat  the  experiment.  Sulphurous 
oxide  was  set  free  instead  of  hydrogen,  and  the  blue  liquid 
contained  the  copper  sulphate.  Perhaps  by  this  time  blue 
crystals  have  made  their  appearance,  but  if  not,  I  evaporate 
the  liquid  to  smaller  bulk  and  let  it  cool.  The  blue  crystals 
are  copper  sulphate. 

Ex.     122. To     PROVE     THAT    THE     BLUE    CRYSTALS     ARE 

COPPER  SULPHATE.  —  I  dissolve  a  crystal  in  water  and 
then  add  ammonia,  as  in  Ex.  91,  and  also  into  another 
portion  of  the  solution  I  put  a  piece  of  iron. 

What  are  the  proofs  that  the  blue  crystals  are  a  com- 
pound of  copper  ? 

I  dissolve  another  crystal  and  add  a  little  hydrochloric 
acid  and  barium  chloride  (Ex.  116). 

What  is  the  proof  that  the  blue  crystals  are  a  compound 
of  sulphuric  acid? 

But  a  compound  of  copper  and  sulphuric  acid  must  be 
the  copper  sulphate :  the  crystals  are  copper  sulphate. 


172  SULPHUR    AND    ITS    COMPOUNDS. 

Different  Ways  to  make  Sulphates.  —  Many  sulphates 
may  be  made  by  the  action  of  the  sulphuric  acid  on  the 
metals  directly.  In  the  case  of  zinc  and  iron  the  action 
goes  on  in  the  cold,  and  yields  hydrogen  beside  the  sul- 
phate. But  in  the  case  of  copper,  heat  must  be  used  to 
produce  the  sulphate,  and  sulphurous  oxide  and  water,  in- 
stead of  hydrogen,  are  set  free. 

Silver,  mercury,  and  some  other  metals  are  like  copper 
in  this  respect.  When  heated  with  strong  sulphuric  acid 
they  yield  sulphates,  sulphurous  oxide,  and  water. 

The  sulphates  may  be  made  also  by  letting  the  acid 
act  on  the  oxides  or  the  hydrates  of  the  metals,  instead 
of  on  the  metals  themselves. 

It  is  also  found  that  this  acid  will  sometimes  yield  two 
salts  of  the  same  metal. 

It  will  do  this  with  sodium,  for  when  the  acid  is  gently 
heated  with  common  salt,  as  in  Ex.  98,  we  get  one  salt 
of  sodium,  but  when  the  heat  is  much  stronger  we  get 
another.  How  can  this  be  ?  Well,  we  see  that  the  mole- 
cule of  the  acid,  H2S04,  has  two  atoms  of  hydrogen,  and 
if  the  heat  be  gentle  an  atom  of  sodium,  Na,  takes  the 
place  of  only  one  of  them,  and  we  have  NaIISO4,  but  if 
the  heat  be  strong  both  atoms  of  hydrogen  are  driven  out 
by  two  of  sodium,  and  we  get  Na2SO4. 

The  first,  NaIISO4,  is  the  acid  sodium  sulphate. 
The  second,  Na2SO4,  is  the  noiinal  sodium  sulphate. 

These  two  kinds  of  salts  may  come  from  any  other 
acid  in  whose  molecules  there  are  two  atoms  of  H,  which 
may  be  driven  out  by  a  metal.  All  such  acids  are 
called  dibasic  acids.  Sulphurous  acid,  H2S03,  and  carbonic 
acid,  H2CO3,  are  dibasic.  They  are  dibasic,  not  because 
they  have  two  atoms  of  H  in  a  molecule,  but  because  they 
have  two  atoms  of  H  which  metals  can  displace. 


SULPHUR    AND    ITS    COMPOUNDS.  173 

Acetic  acid,  H4C202,  is  monobasic.  Its  molecule  con- 
tains four  atoms  of  H,  but  with  metals  it  will  give  up 
only  one. 

An  acid  salt  is  one  which  still  contains  a  part  of  the  hy* 
drogen  which  a  metal  can  displace.  A  normal  salt  is  one 
which  contains  none  of  the  hydrogen  which  a  metal  can 
displace.  The  normal  salts  are  generally  neutral  to  litmus- 
paper,  and  are  often  called  neutral  salts. 

OTHER  SULPHUR  OXACIDS. 

The  sulphurous  and  sulphuric  acids  are  the  most  impor- 
tant oxygen  acids  of  sulphur ;  but  besides  these  two  there 
exists  no  less  than  six  others.  Look  at  their  names  and 
formulas. 


Hyposulphurous  acid,  H2S() 


Pyrosulphuric  acid,    1I2S2<)~ 
Thiosulphuric  acid,    H2  S2  O8 


Dithionic  acid,  H2  S2  O6 
Trithionic  acid,  H2S3O6 
Tetrathionic  acid,  H2S4O6 


Only  one  of  these  needs  to  be  noticed  any  further  at 
present,  and  that  is  the  thiosulphuric  acid.  The  sodium 
salt  of  this  acid  is  very  useful  in  photography :  it  dissolves 
away  from  the  glass  or  paper  the  silver  salts  which  have 
not  been  acted  upon  by  light,  and  which,  if  left,  would 
cause  the  picture  to  blacken.  It  is  known  as  "hyposul- 
phite of  soda,"  but  its  true  name  is  sodium  thiosulphate.  , 

EXERCISES. 

1.    Study  the  action  of  dilute  acids  on   sulphides,  sulphites, 

and  sulphates. 

1.  Put  a  little  of  the  powder  of  some  specimen  of  each 
of  these  compounds  into  a  tube,  moisten  it  with  water,  and 
add  a  little  dilute  hydrochloric  acid.  Watch  for  efferves- 
cence, or  any  other  evidence  of  chemical  action.  Xotice  the 
odor  of  any  gas  which  may  be  set  free.  If  no  action  begins 
soon,  heat  may  be  used. 


174  SULPHUR   AND   ITS    COMPOUNDS. 

2.  Use  dilute  sulphuric  acid,  making  the   experiments 
in  the  same  way. 

3.  Write  a  brief  statement  of  your  results,  pointing  out 
the  differences  in  the  behavior  of  these  three  kinds  of  com- 
pounds. 

2.  Study  the  action  of  barium  chloride  on  sulphites  and  sul- 

phates. 

1.  Add  drops  of  barium  chloride  to  a  solution  of  a  sul- 
phite and  to  a  solution  of  a  sulphate.  Then  compare  the 
precipitates  which  appear. 

£.  Learn,  by  experiment,  whether  these  two  precipi- 
tates are  alike  soluble  in  hydrochloric  acid. 

8.  See  whether  both  these  precipitates  will  appear  if 
you  add  the  hydrochloric  acid  to  the  solutions  before  you 
add  the  barium  chloride.  Compare  Ex.  118. 

4.  Write  a  brief  statement  of  your  results,  pointing  out 
the  difference  in  the  behavior  of  the  sulphites  and  the 
sulphates. 

3.  Take  from  the   teacher,  or  a  friend  who  knows  what 

they  are,  a  few  substances,  and  see  if  you  can  decide 
whether  each  is  a  sulphide,  a  sulphite,  or  a  sulphate. 


PHOSPHORUS,    AND    THE    NITROGEN    GROUP. 

IN  1669  a  man  by  the  name  of  Brandt,  in  Hamburg,  was 
making  experiments,  hoping  to  find  the  "philosopher's 
stone,"  by  the  touch  of  which  he  would  be  able  to  turn 
any  substance  into  gold.  What  he  actually  did  find  was 
a  waxy-looking  solid,  yellow  by  daylight,  but  shining 
with  a  pearly  white  light  in  the  dark.  It  burned  furi- 
ously at  the  least  provocation  by  warmth,  and,  on  the 
whole,  was  so  strange  in  its  actions  that  the  superstitious 
chose  to  name  it  "  The  Son  of  Satan."  It  proved  to  be  an 
element,  and  it  has  since  been  known  as  phosphorus. 

Properties.  —  Phosphorus  comes  to  market  in  the  form 
of  round  "sticks,"  four  or  five  inches  long,  and  about 
a  half-inch  in  diameter.  In  color  it  is  like  yellow  wax, 
but  it  is  much  harder  than  that  substance,  although  soft 
enough  to  be  easily  cut  with  a  knife. 

Its  most  remarkable  property  is  its  strong  attraction  for 
oxygen.  If  brought  into  the  air  it  begins  at  once  to  unite 
with  oxygen,  and  waste  away  by  a  "slow  combustion." 
But  if  gently  heated  at  the  same  time,  its  combustion 
becomes  rapid  and  furious. 

To  rub  it  with  the  warm  fingers  will  inflame  it.  The 
friction  of  a  knife-blade  in  cutting  it  will  sometimes  pro- 
duce heat  enough  to  set  it  on  fire. 

Such  a  substance  can  be  safely  handled  only  when  it  is 
under  water.  It  is  kept  under  water,  and  it  ought  to  be 
cut  under  water,  to  avoid  accident. 

This  element  is  a  powerful  poison. 

Red  Phosphorus.  —  Let  some  phosphorus  be  put  into 
a  vessel  full  of  carbon  dioxide  or  nitrogen,  which  will 
not  act  upon  it,  and  then  let  heat  be  applied.  In  this 

175 


176      PHOSPHORUS,  AND    THE   NITROGEN   GROUP. 

case  the  phosphorus  will  not  burn,  no  matter  how  hot 
it  becomes.  But  at  a  temperature  of  240°  C.  a  curious 
change  takes  place.  "The  melted  phosphorus  becomes 
solid,  opaque,  and  of  a  deep  red  color."  It  is  phosphorus 
in  an  allotropic  form. 

This  "  red  phosphorus "  may  be  exposed  to  the  air  and 
handled  with  very  little  danger. 

The  common  and  the  red  are  not  the  only  allotropic 
forms  in  which  this  extraordinary  element  exists.  There 
is  a  white  and  flaky  form,  lately  discovered  by  Remsen, 
and  a  black  variety  has  been  described  by  Thenard. 

Matches Phosphorus  is  used,  in  large  quantities,  in 

making  friction-matches.  These  are  of  several  kinds, 
among  which  is  the  sulphur  ("Lucifer")  match,  the  par- 
affine  match,  and  the  safety  match. 

The  sulphur  match  is  made  by  dipping  the  end  of  a  pine 
stick  in  melted  sulphur,  and  then  into  a  paste  made  of 
phosphorus  and  a  little  nitre,  KN  03,  mixed  in  gum-water. 
Now,  by  rubbing  the  end  of  the  match,  we  produce  heat 
enough  to  set  the  phosphorus  on  fire ;  the  burning  of  the 
phosphorus  produces  more  heat,  by  which  the  sulphur  is 
set  on  fire,  and  then  the  sulphur  burning  with  still  more 
heat  sets  fire  to  the  wood. 

The  paraffine  match  is  made  in  the  same  way,  but  par- 
affine  is  used  instead  of  sulphur. 

In  this  way  the  troublesome  odor  (S  O2)  of  burning 
sulphur  is  avoided.  Sometimes  potassium  chlorate  is  used 
in  the  mixture,  and  then  the  match  burns  with  a  slight 
explosion. 

The  safety-match  has  no  phosphorus  in  its  tip;  this 
element  is  spread  on  the  side  of  the  box  instead.  Red 
phosphorus  is  used.  The  match-stick  is  tipped  with  a 
mixture  of  sulphur  or  antimony  sulphide,  and  potassium 
chlorate,  and  sometimes  red  lead  or  some  other  coloring 
substance  is  added. 


PHOSPHORUS,  ANl>    THE  NITROGEN   GROUP.       177 

To  "light"  this  match,  it  must  be  rubbed  against  the 
phosphorus  surface  of  the  box. 

Phosphorus  Oxides.  —  There  are  two  compounds  of 
this  element  with  oxygen. 

Phosphorus  oxide ^2O3 

Phosphoric  oxide I*aO5 

The  first  is  made  when  phosphorus  is  simply  exposed 
to  the  air.  The  second  is  made  by  burning  phosphorus 
in  oxygen  or  air. 

Let  a  small  piece  of  phosphorus  be  hung,  by  a  fine  wire, 
inside  a  bottle ;  white  vapors  of  P2  O3  will  fall  from  it  and 
slowly  fill  the  bottle.  If  then  a  little  water  is  shaken  in 
the  bottle,  some  of  these  vapors  are  dissolved,  and  by 
adding  a  few  drops  of  blue  litmus  solution,  we  prove  the 
presence  of  an  acid.  Thus: 

Phosphorus  oxide  .  .  P2  O3  -f  3  H2  O  =  2  H3  P  O3  .  .  Phosphorus  acid. 

Let  a  small  piece  of  dry  phosphorus  be  placed  on  a  little 
cup  on  a  plate.  Let  it  be  touched  with  a  hot  wire,  and 
immediately  covered  with  a  dry  glass  jar.  Clouds  of  milk- 
white  vapor  are  quickly  formed,  and,  if  everything  is  dry, 
snow-white  flakes  will  soon  be  seen,  some  clinging  to  the 
walls  of  the  jar,  others  falling  like  snow  upon  the  plate. 
This  snow-white  solid  is  phosphoric  oxide,  P2O5. 

Let  a  little  water  be  poured  on  the  plate,  and  the  white 
solid  will  instantly  dissolve  with  a  hissing  sound,  like  the 
sound  of  a  hot  iron  in  water.  A  little  blue-litmus  is  red- 
dened by  this  solution,  proving  the  presence  of  an  acid. 
Thus: 

Phosphoric  oxide  .  .  P2  O5  -f-  3  H2  O  =  2  H3  P  O4  .  .  Phosphoric  acid. 

There  is  a  third  acid  in  this  series ;  it  is  the  hypo- 
phosphorus  acid,  H3P02.  But  of  these  three  we  shall 


178      PHOSPHORUS,  AND    THE  NITROGEN   CROUP. 

notice  further  only  the  phosphoric  acid,  which  is  important 
on  account  of  its  useful  salts,  —  the  phosphates. 

The  Phosphates.  —  These  are  found  in  rocks  and  soils, 
in  plants  and  in  animals.  It  is  in  the  form  of  phosphate 
that  phosphorus  exists  most  largely  in  nature.  We  find 
it  more  abundant  in  the  seeds  of  plants  than  in  other  parts, 
and  in  the  brain,  the  blood,  and  the  bones  of  animals ;  and, 
accordingly,  we  find  that  the  phosphates  are  much  used  to 
fertilize  soils  on  which  grain  is  to  grow,  and  that  they 
are  also  needful  constituents  in  the  food  of  man. 

Manufacture  of  Phosphorus Phosphorus  is  itself 

extracted  from  bones.  Almost  half  the  weight  of  the 
bones  in  animals  is  calcium  phosphate,  Ca^  (PO4)2,  and 
about  one-fourth  of  the  weight  of  this  phosphate  is  pure 
phosphorus. 

If  the  skeleton  of  a  man  weighs  12  Ibs.  it  contains  about 
one  and  a  half  pounds  of  this  element. 

To  obtain  phosphorus  from  bones  they  are  first  burned ; 
in  this  process  they  become  very  white  and  very  brittle. 
They  are  afterwards  crushed  to  powder;  this  powder  is 
called  bone-ash,  and  it  is  chiefly  calcium  phosphate. 

From  the  bone-ash  the  phosphorus  is  obtained1  by 

1.  Treating  it  with  sulphuric  acid. 

2.  Evaporating  the  solution  to  dryness. 

3.  Heating  the  residue  nearly  to  redness. 

4.  Heating  to  redness  with  charcoal. 

ARSENIC. 

The  element  arsenic  is  a  solid  substance  with  a  steel- 
gray  color,  and  a  luster  like  the  metals.  It  is  very  brittle 
and  easily  powdered.  Its  powder  is  sometimes  sold  under 
the  false  name  "cobalt,"  to  be  used  as  a  fly-poison. 

1  For  details  and  explanations  consult  Roscoe  and  Schorlemmer, 
Vol.  I.  p.  460. 


PHOSPHORUS,  AND   THE  NITROGEN   GROUP.      179 

This  element  is  sometimes  found  in  the  earth  not  com- 
bined with  anything,  but  such  native  arsenic,  as  it  is  called, 
is  not  common.  It  is  mostly  found  in  combination  with 
metals  and  sulphur. 

In  Silesia,  Germany,  there  is  found  a  mineral  which  con- 
tains arsenic  with  iron  and  sulphur ;  it  is  called  mispickel, 
and  its  formula  is  Fe  As  S.  This  mineral  is  the  source 
from  which  most  of  the  arsenic  of  commerce  is  obtained. 

The  chief  use  of  arsenic  is  in  making  shot.  A  small 
quantity  of  the  element  is  melted  with  the  lead.  Lead 
alone  is  too  soft ;  the  arsenic  hardens  it. 

Arsenous  Oxide.  —  This  is  the  principal  compound  of 
arsenic  in  commerce.  Its  formula  is  As203,  and  it  is  also 
called  arsenic  trioxide,  because  its  molecule  contains  three 
atoms  of  oxygen.  In  the  drug-stores  it  is  often  called 
white  arsenic,  but  more  generally  simply  "  arsenic." 

This  oxide  is  made  directly  from  arsenical  pyrites, — 
another  name  for  mispickel. 

To  get  the  oxide  from  mispickel  the  mineral  is  roasted, 
that  is  to  say  it  is  heated  in  a  current  of  air.  The  hot  oxy- 
gen of  the  air  takes  the  arsenic  from  the  hot  mineral,  and 
the  two  elements  combine ;  arsenous  oxide  is  the  result. 

This  substance  is  a  white  solid;  it  can  be  dissolved  in 
hot  water,  in  cold  water  not  so  well.  Its  solution  is  almost 
tasteless  and  colorless,  and  without  odor.  It  is  a  most 
fearful  poison. 

But  while  this  compound  is  so  fatal  to  the  life  of  an 
animal,  it  has  a  strange  power  to  prevent  decay.  It  is 
used  to  destroy  rats,  mice,  insects,  and  sometimes  for  the 
terrible  purpose  of  taking  the  lives  of  men.  On  the  other 
hand,  it  is  made  to  do  good  service  in  the  preservation  of 
the  stuffed  or  dried  objects -of  natural  history  to  be  found 
in  museums. 

Arsenous  oxide  is  an  anhydride,  that  is  to  say,  it  be- 


180       PHOSPHORUS,  AND   THE  NITROGEN   GROUP. 


comes  an  acid  by  combining  with  the  elements  of  water. 
By  so  doing  it  forms  arsenous  acid.     Thus : 

As2O3  +  3H2O  =  2H3AsO3 

From  this  arsenous  acid,  H3AsO3,  a  large  number  of 
salts,  —  the  arsenites,  may  be  made.  Sodium  arsenite  is 
very  useful  in  calico-printing;  it  helps  to  "fix"  the  color, 
—  in  other  words,  prevent  its  fading.  The  common  Paris- 
green  is  copper  arsenite  and  copper  acetate  together. 

Arsenic  Oxide.  —  There  is  also  arsenic  oxide ;  its  for- 
mula is  As2  05.  It  is,  like  the  other,  an  anhydride,  for  with 
water  it  yields  arsenic  acid,  H3AsO4. 

Arsenic  and  Hydrogen.  —  There  is  one  compound  of 
these  two  elements,  a  gas  called  arsine.  It  is  made  by  the 
action  of  nascent  hydrogen  on  a  soluble  compound  of  arsenic. 
It  is  very  poisonous;  Gehlen,  who 
discovered  it,  lost  his  life  by  acci- 
dentally breathing  a  bubble  of  this 
gas.  It  burns  freely,  and,  if  made 
in  the  laboratory,  it  should  be  burned 
as  fast  as  it  forms. 

Ex.   123.  —  To    make    and    burn 
this  gas  I  use  the  simple  hydrogen- 
flame   apparatus   of   Ex.  20,  shown 
again   in   Fig.   62.     Before  putting 
the  zinc  into  the  hydrochloric  acid 
in  the  mortar  to  ma'ke  the  hydro- 
gen, I    dissolve    a   little    arsenous 
oxide   in  water,  by  putting  a  very 
little    of    the    powder  —  not   more 
than  will  lie  on  the  tip  of  a  penknife-blade  —  into  one  or 
two  cubic  centimeters  of  water  in  a  test-tube  and  boiling  it. 
I  then  drop  several  fragments  of  zinc  into  the  dilute 
acid  in  the  mortar,  and  at  once  lower  the  funnel  to  cover 


Fij.  62. 


PHOSPHORUS,  AND    THE  NITROGEN  GROUP.      LSI 

them.  Hydrogen  is  rapidly  set  free.  It  drives  the  air  out 
of  the  apparatus,  and  when  this  is  done  I  set  fire  to  the 
jet.  I  now  hold  the  bottom  of  a  cleata,  dry  porcelain  dish 
right  across  the  flame  for  a  moment ;  no  dark  stain  should 
be  left  upon  it. 

Then  I  pour  the  arsenous  oxide  solution  into  the  mortar. 
Very  soon  the  color  of  the  flame  becomes  bluish-white. 
Again  I  press  the  cold  porcelain  for  a  moment  down  into 
the  flame ;  a  lustrous  brown  stain  is  left  upon  it.  I  let 
the  flame  play  on  other  parts  of  the  dish,  touching  it  here 
and  there  on  the  inside  also.  A  large  surface  may  be  thus 
covered  with  the  brown  arsenical  mirror. 

At  the  moment  when  hydrogen  is  set  free  by  the  zinc 
it  attacks  the  arsenous  oxide  and  changes  the  arsenic  into 
arsine,  AsH3,  and  its  oxygen  into  water. 

The  arsine  burns  with  a  livid  flame,  thus : 

2AsH8  +  60rrAs203  +  3H2O 

arsenous  oxide  and  water  being  the  products  of  the  action. 
But  the  cold  porcelain  cools  the  flame,  and  then  only  the 
hydrogen  of  the  arsine  burns,  while  the  arsenic  is  deposited 
on  the  dish  in  the  form  of  a  lustrous  mirror.  This  mirror 
will  appear,  even  when  the  quantity  of  arsenic  used  in  the 
experiment  is  astonishingly  small.  In  fact,  this  experi- 
ment is  a  most  excellent  way  of  testing  for  arsenic  in  any 
suspicious  substance.  It  is  known  as  Marsh's  test. 

The  chemist  has  studied  the  compounds  of  arsenic,  until 
he  has  so  well  learned  their  characters,  that  he  can  tell  with 
great  certainty  whether  they  are  present  in  a  substance  or 
not,  and  Marsh's  test  is  his  most  trusted  method.  It  is 
true  that  antimony  will  also  give  a  stain  on  porcelain  in 
the  same  way,  but  its  color  is  velvety  black,  and  there  are 
other  well-marked  differences  which  are  well  known  to 
every  practical  chemist. 


182      PHOSPHORUS,  AND    THE  NITROGEN  GROUP. 


THE    NITROGEN    GROUP. 

PHOSPHORUS  and  arsenic  are  much  alike  in  their  chemi- 
cal actions,  and  in  some  things  both  resemble  nitrogen: 
these  three  are  the  members  of  the  nitrogen  group  of  non- 
metals. 

Their  Hydrogen  Compounds.  —  These  elements  unite 
with  hydrogen,  and  in  the  same  proportions.  The  names 
and  formulas  of  their  compounds  plainly  show  this  fact. 
We  have 

Ammonia  (amine) .     .     H3  N 

Phosphine H3P 

Arsine H3  As 

We  see  that,  in  this  group,  each  element  unites  with 
hydrogen,  one  atom  for  three.  In  other  respects  the 
resemblance  among  them  is  not  so  striking  as  it  is  in  the 
chlorine  group  or  in  the  sulphur  group. 

The  order  of  their  atomic  weights  is  as  follows: 

N  P  As 

14  31  75 

This  is  also  the  order  of  their  densities.  The  strength 
of  their  attraction  for  hydrogen  is  less,  as  the  atomic 
weight  is  greater,  in  the  same  order.  But  among  these 
elements  the  relation  of  properties  to  atomic  weights  is 
not  so  close  as  in  the  cases  of  the  chlorine  and  the  sul- 
phur groups. 


,    AND    THE    CARBON    GROUP. 

Silicon.  —  The  element  silicon  is  in  many  respects  very 
much  like  carbon. 

It  is  usually  a  dark-colored  powder,  but  it  has  two  other 
forms,  which  are  a  little  like  graphite  and  diamond. 

Silicon,  next  to  oxygen,  is  the  most  abundant  element 
in  the  world,  but  it  is  never  found  alone ;  it  is  combined 
with  oxygen,  and  the  two  are  not  easily  separated.  Im- 
mense quantities  of  silicon,  in  this  condition,  are  hidden  in 
the  sandstone  rocks,  so  very  common,  yet  very  few  persons 
who  are  not  chemists  have  ever  seen  the  element  itself. 

Its  Oxide.  —  The  compound  of  silicon  and  oxygen  is 
known  as  silica.  Its  true  chemical  name  is  silicon  dioxide ; 
its  formula  is  Si02.  Common  sand  is  chiefly  silica,  and 
the  sandstone  rocks  are  masses  of  silica,  mixed  with  many 
impurities  to  be  sure,  but  chiefly  silica.  And  besides,  there 
are  many  purer  forms,  such  as  the  following: 

Flint  is  a  kind  of  very  hard  stone  which  is  sometimes 
white,  sometimes  brown  or  black,  but  it  is  always  silica, 
and  a  much  purer  form  than  sandstone.  In  some  places 
very  fine  transparent  diamond-shaped  crystals  are  found ; 
they  are  called  rock-crystal,  and  consist  of  pure  silica. 
The  common  name  of  these  hard  varieties  of  silica  is 
quartz. 

The  beautiful  amethyst  is  quartz  crystal,  with  a  delicate 
purple  color. 

The  precious  opal,  the  chrysoprase,  and  the  bloodstone 
are  little  else  than  silica. 

Jasper  is  a  very  fine-grained  form  of  silica,  colored  gen- 
erally red,  but  sometimes  black. 

183 


184  SILICON,    AND    THE    CARBON    GROUP. 

The  agate  is  a  form  of  silica  in  which  many  tints  of 
color  are  delicately  arranged  in  stripes  or  bands.  When 
the  colors  are  few  and  very  regularly  arranged  the  agate 
is  called  an  onyx.  When  the  color  is  uniform,  and  a 
pearly  white,  the  stone  is  a  chalcedony,  but  when  red  it 
is  called  carnelian. 

THE  CARBON  GROUP. 

Silicon  behaves  very  much  like  carbon  in  its  chemical 
actions.  The  two  are  much  more  like  each  other  than 
like  any  other  non-metals,  and  they  together  are  called 
the  carbon  group. 

Their  Hydrogen  Compounds. — These  elements  unite 
with  hydrogen  in  the  same  proportions.  They  yield 

Methane  (carbon  hydride)  .    ,    .    .    ,    .    .     .     .   C  H4 
Silicon  hydride  .     .     .     *•    /;;:*>  v<.;>.   ..;.-:.     .   Si  H4 

We  see  that,  in  this  group,  each  element  unites  with 
hydrogen,  one  atom  with  four. 

Their  Oxygen  Compounds They  are  not  only  alike 

in  their  combination  with  hydrogen,  but  also  with  oxygen, 
for  we  have  carbon  dioxide,  C  O2,  and  silicon  dioxide,  SiG2. 
And  then,  just  as  from  carbon  dioxide  we  get  carbonic 
acid,  by  its  union  with  water,  thus : 

C02         +        H20        =        H2C03 

The  dioxide  Water  The  acid 

so  from  silicon  dioxide  we  get  silicic  acid, 
Si02        +        II20        =        H2Si03 

The  dioxide  Water  The  acid 

The  likeness  does  not  stop  here,  for  just  as  carbonic 
acid  yields  salts  —  the  carbonates,  so  silicic  acid  yields 
salts — the  silicates. 

The  Silicates.  —  These  salts  are  very  abundant   in  na- 


SILICON,    AND    THE    CARBON    GROUP.  185 

ture,  and  very  useful  in  the  arts.  The  natural  silicates 
occur  in  soils  :  clay  is  one  of  them.  They  also  make  up 
large  rock  masses  :  the  slates  are  of  this  kind.  Clay  and 
the  slate  rocks  alike  are  made  chiefly  of  aluminum  silicate. 

Artificial  silicates  are  easily  made.  It  is  only  necessary 
to  melt  together  some  silica,  —  say  fine  white  sand,  and 
potassium,  or  sodium,  or  calcium  carbonate,  to  produce 
the  potassium,  sodium,  or  calcium  silicate.  These  arti- 
ficial silicates  are  called  glass. 

In  each  different  kind  of  glass  there  are  at  least  two 
kinds  of  silicate.  In  common  "window  glass"  there  are 
sodium  and  calcium  silicates;  in  "flint  glass"  there  are 
potassium  and  lead  silicates.  Most  ornamental  glassware, 
such  as  vases,  fine  goblets,  and  decanters,  are  made  of 
flint  glass.1 

BORON. 

The  Element  —  The  element  boron  can  be  obtained 
in  two  forms  ;  as  a  dark-brown  powder  and  as  fine  crys- 
tals, almost  as  hard  as  diamond.  It  is  never  found  free 
in  nature,  but  some  of  its  compounds  are  quite  abundant 
The  most  interesting  are  boric  acid  and  borax. 

Borax.  —  There  is  a  lake  in  California  (Borax  Lake) 
whose  waters  hold  a  large  quantity  of  borax  in  solution, 
and  borax  for  the  market  is  obtained  by  evaporating  this 
water.  It  comes  out  in  the  form  of  a  mass  of  white 
crystals.  The  chemical  name  of  this  substance  is  sodium 
biborate.  But  the  pure  and  dry  biborate  is  not  quite  the 
same  as  the  crystals,  for  they  hold  a  large  portion  of  water 
in  combination,  while  the  biborate  has  none. 

This  is  shown  by  the  formulas,  — 


Sodium  biborate      ........     Xa2  B4  O7 

Borax  crystals     .     .     .     ......     Na2  B4  O7  +  10  H2  O 

1  Roscoe  and  Schorlemmer,  Vol.  II.,  Ft.  I.,  pp.  462  to  490. 


186  SILICON,    AND    THE    CAKBON    GROUP. 

Now,  this  water  is  a  part  of  the  crystal,  for  if  we 
it  away  by  heat  the  borax  is  no  longer  crystalline.  This 
water  is,  therefore,  called  the  water  of  crystallization.  The 
crystals  of  a  great  many  other  things  also  hold  water  of 
crystallization. 

Ex.  124.  —  I  make  a  solution  of  5  g.  of  borax  in  20  cc. 
of  hot  water  in  a  porcelain  dish,  and  then  add  to  it,  in 
small  portions,  1  cc.  strong  sulphuric  acid.  I  let  this  stand 
until  cold.  Then  notice  and  describe  the  crystals  which 
form.  Are  they  crystals  of  borax  ? 

Ex.  125.  —  To  answer  this  question  I  put  some  of  the 
crystals  into  one  porcelain  dish,  and  as  much  borax  into 
another,  and  pour  upon  each  10  cc.  of  strong  alcohol.  I  stir 
them  well,  and  then  fire  them  both  with  a  match-flame,  and 
notice  the  color  of  the  flames,  especially  around  the  edges. 

What  evidence  that  the  crystals  are  not  borax  ? 

Boric  Acid.  —  Borax  is  changed  to  boric  acid  by  the 
action  of  strong  sulphuric  acid.  Boric  acid  when  dry  ap- 
pears in  the  form  of  glistening  scale-like  crystals  (Ex.  124). 
These  dissolve  in  alcohol,  and  tinge  the  flame  of  alcohol 
with  green  (Ex.  125). 

Boric  acid  is  sometimes  made  on  a  large  scale  in  this 
way,  that  is  by  the  action  of  a  strong  acid  on  borax.  But 
it  is  also  obtained  by  evaporating  natural  waters  which  hold 
it  in  solution.  Such  water  is  found  in  Tuscany.  It  is  in 
a  volcanic  region,  and  jets  of  volcanic  steam,  out  of  the 
earth,  are  directed  into  this  water.  The  water  evaporated 
by  the  volcanic  heat  leaves  boric  acid. 

No  Hydrogen  Compound.  —  Boron  is  the  only  non- 
metal  which  does  not  combine  with  hydrogen.  We  have 
seen  that  elements,  which  combine  with  hydrogen  in  the 
same  way,  are  very  much  alike  also  in  most  of  their  chem- 
ical actions.  Now  here  is  an  element  which  seems  to  have 


SILICON,    AND    THE    CARBON    GROUP.  187 

no  disposition  at  all  to  unite  with  hydrogen,  and,  curiously 
enough,  we  find  it  standing  apart  from  all  the  other  non- 
metals  in  other  respects  too.  When  free,  it  is  a  little  like 
carbon  and  silicon.  In  some  of  its  properties  it  resembles 
the  nitrogen  group;  in  others  it  is  more  like  the  metals 
than  the  non-metals. 

Boron  does  not  fairly  belong  to  either  group  of  non- 
metals,  but  on  the  whole  it  stands  nearer  to  the  nitrogen 
group  than  to  others,  and  it  is  usually  named  in  the  list 
of  that  group. 

But,  in  both  its  forms,  it  differs  from  the  members  of 
that  group.  For  example :  the  crystallized  variety  will 
not  readily  combine  with  oxygen,  while  the  elements  of 
the  nitrogen  group,  except  nitrogen  itself,  will ;  and  the 
other  variety  —  the  brown  powder  —  when  heated  to  red- 
ness, will  combine  with  nitrogen ;  this  the  other  members 
of  the  nitrogen  group  will  not  do. 


VAI/ENCE. 

WE  have  seen  that  every  one  of  the  non-metals,  except 
boron,  will  combine  with  hydrogen.  But  we  have  found 
that  they  do  not  all  combine  with  it  in  the  same  propor- 
tions. In  some  cases  they  combine  with  it,  atom  for  atom 
(p.  150),  in  others  one  atom  for  two  (p.  162),  and  in  other 
cases  the  proportions  are  still  different  (pp.  182,  184). 
What  is  the  meaning  of  this  ? 

A  Difference  in  Atoms.  —  The  proportions  of  the  ele- 
ments, in  these  compounds  of  the  non-metals  with  hydro- 
gen, are  found  by  actual  analysis,  and  then  they  may  be 
shown  by  their  formulas,  each  symbol  of  an  element 
standing  for  one  combining  weight.  Let  us  take  one 
formula  from  each  of  the  four  groups  which  we  have 
studied,  as  an  example, — 

HC1  H20  H8N  H4C 

and  we  see  that  one  combining  weight  of  chlorine  combines 
with  one  of  hydrogen,  but  that  one  of  oxygen  is  not  sat- 
isfied with  so  little ;  it  must  have  two.  One  combining 
weight  of  nitrogen  refuses  to  unite  with  less  than  three  of 
hydrogen,  while  one  of  carbon  demands  four. 

But  we  may  as  well  say  atoms,  as  combining  weights, 
for,  by  the  atomic  theory,  a  combining  weight  of  an  ele- 
ment represents  one  atom.  If  so,  the  formulas  show  that 
one  atom  of  chlorine  can  hold  one  atom  of  hydrogen, 
that  an  atom  of  oxygen  is  able  to  hold  two,  while  an 
atom  of  nitrogen  is  able  to  hold  three,  and  an  atom  of 
carbon,  still  more  powerful,  is  able  to  hold  four.  In  this 
way  it  appears  that  these  atoms  differ  in  their  power  to 
hold  atoms  of  hydrogen  in  combination  in  a  molecule. 


VALENCE.  189 

VALENCE.  —  Now  this  power  of  an  atom  to  hold  a  defi- 
nite number  of  other  atoms  in  a  molecule  is  called  its 
valence.1 

The  valence  of  an  atom  is  measured  by  the  number  of 
hydrogen  atoms  which  it  can  hold  in  combination.  Thus 
the  valence  of  chlorine  is  1,  of  oxygen  is  2,  of  nitrogen 
is  3,  and  of  carbon  is  4. 

The  valence  of  an  atom  is  described  by  a  prefix.  Thus 
chlorine  is  said  to  be  uratvalent,  oxygen  fa'valent,  nitrogen 
fr'ivalent,  and  carbon  quadrivalent. 

The  valence  of  an  atom  is  shown  to  the  eye  usually  by 
primes  or  dashes,  written  with  the  symbol,  thus : 

Cl'    or  Cl_  shows  that  chlorine  is  a  univalent  element. 
()"    "    O  =      "        "     oxygen      "    bivalent  " 

X'"  "    N=      "         "     nitrooren    "    trivalent          " 


(j""  «    (j  =      »         «     carbon       "    quadrivalent  " 

The  place  of  the  dashes  is  of  no  consequence ;  they  may 
be  written  above  the  symbol,  below,  at  the  right,  or  at 
the  left  of  it.  Thus : 

Cl—  — O—  — N—  — C— 

It  is  the  number  of  dashes  which  shows  the  valence  of 
the  element. 

Substitution  is  Governed  by  Valence.  —  Chlorine 
will  take  the  place  of  hydrogen  in  methane.  To  bring  this 
about  it  is  only  necessary  to  mix  the  two  gases  and  put  the 
mixture  in  diffuse  light.  When  this  is  done,  it  is  found 
that  the  chlorine  will  take  the  place  of  the  hydrogen  grad- 
ually, until  none  is  left.  Methane,  CH4,  may  as  well  be 
written  C  H  H  H  H.  Then  it  is  found  that, — 

1  This  property  is  also  called  quantivalence,  and  equivalence,  and 
valency,  by  different  writers.  To  call  it  valence  is  one  of  the  later 
suggestions,  and  one  worthy  of  general  adoption. 


190  VALENCE. 

C  HH  II  H  is  first  changed  to  C  II  H  II  Cl 
CHHHC1  "  then  "  «  CHHC1C1 
CHHC1C1  "  «  "  «  CHC1C1C1 

CHC1C1C1  "      "  "        "    CC1C1C1C1 

Notice  that  the  substitution  of  Cl  for  H  goes  on  grad- 
ually, atom  for  atom.  The  carbon  gives  one  atom  of  hydro- 
gen for  one  of  chlorine  every  time.1 

The  chlorine  and  hydrogen  atoms  have  the  same  valence. 
Like  bronze  and  copper  pennies,  they  are  different  kinds 
of  matter,  but  have  the  same  value  in  making  change. 
One  atom  of  chlorine  may  be  exchanged  for  one  atom  of 
hydrogen,  and  no  more,  in  any  chemical  action.  In  fact, 
all  univalent  substances  displace  one  another  atom  for 
atom. 

But  a  bivalent  atom  is  worth  as  much  as  two  univalent 
atoms,  and,  in  chemical  action,  the  exchange  must  be  made 
one  atom  for  two.  So  one  quadrivalent  atom  is  worth  two 
that  are  bivalent,  and  two  trivalent  atoms  are  worth  three 
that  are  bivalent,  in  all  chemical  changes. 

What  is  the  Valence  of  Boron?  —  Boron  will  not  com- 
bine with  hydrogen,  but  it  will  with  chlorine.  The  chlo- 
ride is  BC13.  Here  we  see  one  atom  of  boron  holding 
three  univalent  atoms  of  chlorine,  which  shows  that  boron 
is  trivalent. 

In  this  way  the  valence  of  many  other  elements  has  been 
found ;  if  they  have  no  hydrogen  compounds  their  chlorine 
compounds,  or  their  compounds  with  some  other  element 
whose  valence  is  known,  may  be  used  instead.  The  val- 
ence of  the  metals  has  been  found  in  this  way. 

Valence  Useful  in  Writing  Reactions The  valence 

of  the  elements  tells  us  how  many  atoms  must  take  part 
in  a  reaction,  and  helps  one  to  see  how  many  molecules  of 

1  The  H  which  is  driven  out  combines  with  other  atoms  of  Cl  to 
form  HC1. 


VALENCE.  191 

each  substance  are  involved  in  the  change  which  goes  on. 
For  example : 

We  have  found  that  sodium  with  hydrochloric  acid  yields 
sodium  chloride  and  hydrogen  (Ex.  76).  But  sodium  is 
univalent,  and  so  we  write 

Na'  +  H'Cl'^NaCl  +  H 

So  also  zinc  and  hydrochloric  acid  yield  zinc  chloride 
and  hydrogen  (Ex.  78).  Shall  we  write 

Zn  +  HC1  =  ZnCl  +  H 

No,  because  zinc  is  bivalent ;  one  atom  of  zinc  is  worth 
two  atoms  of  hydrogen,  and  must  take  the  place  of  two. 
But  there  is  only  one  in  one  molecule  of  H  Cl,  and  there- 
fore we  must  write 

Zn"  +  2H'Cr  =  Zn"Cl'2-f  2H 

Many  reactions  already  studied  will  now  seem  clearer  in 
the  light  of  this  explanation,  furnished  by  valence,  and 
in  the  future  study  of  chemical  actions  valence  will  help 
us  much. 

The  Valence  of  an  Element  changes But  the  val- 
ence of  the  same  element  is  not  always  the  same.  It  de- 
pends partly  on  the  other  substance  with  which  it  acts. 
Sulphur  is  bivalent  with  hydrogen,  H2S",  but  it  is  quad- 
rivalent with  oxygen  S'V0"2.  And  nitrogen,  a  trivalent 
element,  sometimes  has  a  valence  of  five.  Still  the  changes 
in  valence  are  very  regular,  and  they  do  riot  greatly  hinder 
our  using  valence  as  a  guide  in  writing  common  reactions. 


METALS. 

What  is  a  Metal? — We  think  of  a  metal  as  a  sub- 
stance which  is  heavy,  hard,  and  lustrous,  and  a  good 
conductor  of  electricity  and  heat,  because  most  of  the 
common  metals  have  these  properties  in  high  degree. 

But  there  are  some  metals  which  are  as  soft  as  wax  and 
lighter  than  water.  In  some  conditions,  metals  are  not 
at  all  lustrous,  and  some  are  not  very  good  conductors. 
We  must  look  further  than  to  these  properties  for  a  real 
difference  between  metals  and  non-metals.  It  will  be  found 
in  their  chemical  actions. 

The  compounds  of  other  non-metals  with  hydrogen  and 
oxygen  are  acids,  while  the  compounds  of  metals  with 
hydrogen  and  oxygen  are  bases.  Remember  that  acids 
and  bases  are  just  opposite  in  character,  and  yet  both 
contain  hydrogen  and  oxygen.  The  other  element  which 
is  combined  with  these  two  must  be  very  different,  in 
order  to  make  an  acid  in  one  case  and  a  base  in  another. 
And  those  which  form  the  acids  are  the  non-metals,  while 
those  which  form  the  bases  are  the  metals. 

A  metal  is  an  element  whose  compound  with  hydrogen  and 
oxygen  is  a  base. 

There  is  another  chemical  action  in  which  metals  and 
non-metals  differ.  Remember  what  has  been  said  about 
salts,  that  they  are  made  by  putting  another  element 
into  an  acid  in  place  of  the  hydrogen.  Now,  these  ele- 
ments which  can  take  the  place  of  the  hydrogen  in  acids 
are  the  same  ones  which,  united  with  hydrogen  and  oxy- 
gen, form  the  bases;  they  are  the  metals.  This  gives  us 
another  definition: 

192 


METALS.  193 

A  metal  is  an  element  which  will  take  the  place  of  hydro- 
gen in  an  acid  and  form  a  salt. 

Accordingly  the  chemist  divides  the  seventy-one  elements 
into  two  classes,  metals  and  non-metals,  and  in  a  general 
way  the  division  is  right.  But  nature  does  not  draw  any 
such  sharp  line  of  division  through  the  list  of  elements. 
There  are  some  elements  whose  compounds  with  hydrogen 
and  oxygen  are  sometimes  bases  and  sometimes  acids. 
This  is  true  of  iron.  The  fact  is,  that  while  some  of  the 
elements  are  perfect  non-metals,  and  some  are  perfect 
metals,  there  lie,  between  these,  others  which  are  less  and 
less  perfect,  and  some  which  are  almost  as  much  one  as 
the  other.  In  nature  there  is  a  gradual  difference,  in  the 
properties  of  the  elements,  running  from  one  end  of  the 
list  to  the  other. 

Number  and  Abundance  of  the  Metals.  —  We  have 
seen  that  the  non-metals  are  included  in  four  groups,  and 
that  they  number  only  fifteen.  All  others  of  the  seventy- 
one  elements  are  metals. 

Most  of  this  large  number  of  metals  are  rare  substances 
seldom  seen  or  little  used.  Not  more  than  fifteen  or 
twenty  are  abundant  in  nature  or  useful  in  the  arts. 

In  our  study  of  the  metals  we  will  select  those  which 
will  teach  us  the  most  chemistry,  are  the  most  abundant, 
and  the  most  useful.  The  study  of  the  complete  list  of 
metals  and  their  compounds  need  be  attempted  only  by 
students  who  are  to  become  chemists.  To  such  this  pres- 
ent course  is  simply  a  preparation. 

Occurrence  of  Metals  in  Nature There  are  a  few 

metals  which  are  sometimes  found  free  in  the  earth,  not 
pure,  but  simply  mixed  with  other  things.  Gold  and 
silver  and  copper  are  examples.  Metals  when  found  in 
this  condition,  uncombined  with  other  elements,  are  called 
native  metals. 


194  METALS. 

But  the  metals  are  usually  found  in  combination  with 
non-metals.  In  fact,  the  solid  earth  is  made  up  of  such 
compounds.  But  the  rocks  generally  contain  so  much 
besides  these  compounds,  or  it  is  so  difficult  to  get  the 
metals  out  of  them,  that  they  are  worthless  for  this  pur- 
pose. 

There  are,  however,  some  parts  of  the  rocky  masses, 
which  are  made  up  of  metallic  compounds,  so  rich  in  metal 
that  they  are  valuable  substances  from  which  to  get  the 
metals  themselves.  Such  compounds  of  the  metals  are 
called  ores. 

The  work  of  taking  these  ores  out  of  the  earth  is 
mining,  and  that  of  getting  the  metal  out  of  the  ore  is 
metallurgy.  Mining  is  a  mechanical  operation,  and  we 
will  not  stop  to  describe  it,  but  metallurgy  is  a  chemical 
art,  and  we  will  study  it  in  connection  with  several  of 
the  common  and  the  useful  metals  when  we  reach  them, 
as  a  good  example  of  the  application  of  chemistry  to 
useful  purposes. 

The  most  valuable  ores  of  the  metals  are  the  oxides, 
the  sulphides,  the  chlorides,  and  the  carbonates. 


THE    POTASSIUM    GROUP. 

POTASSIUM.    JF. 

Description  of  the  Metal.  —  Most  metals  are  very  hard, 
but  potassium  is  as  soft  as  wax.  It  is  easily  moulded  by 
the  fingers  or  cut  with  a  knife.  When  freshly  cut,  the  sur- 
face shines  with  a  blue-white  luster. 

Most  metals  are  heavy,  but  this  one  is  lighter  than 
water.  A  piece  dropped  on  water  will  float  like  cork. 
Nor  is  this  the  only  thing  that  will  surprise  one,  who  for 
the  first  time  drops  potassium  on  water;  the  metal  will 
instantly  take  fire.  Violet-colored  flames  will  burst  from 
it,  while  the  melted  globule  will  run  wildly  over  the  water, 
wasting  away  all  the  time,  until,  when  nearly  all  gone,  it 
will  usually  put  a  stop  to  the  action  by  a  small  explosion. 

Its  Chemical  Action  on  Water The  product  of  this 

action  is  found  to  be  a  base.  (How  would  you  prove  it  ?) 
It  is  the  potassium  hydroxide.  We  may  write  the  reaction 

II  HO      +      K  KHO        +         H 

Water  Potassium1          Potassium  hydroxide       Hydrogen 

The  atom  of  potassium  is  univalent.  It  takes  the  place 
of  one  of  the  two  atoms  of  hydrogen  in  a  molecule  of  water, 
and  forms  a  molecule  of  the  hydroxide. 

Hydrogen  and  much  heat  are  also  set  free ;  in  fact,  heat 
enough  to  set  the  hydrogen  on  fire.  A  little  of  the  potas- 
sium itself  also  burns,  and  it  is  this  which  gives  violet  color 
to  the  flame. 

Occurrence  in  Nature Compounds  of  this  metal 

are  present  in  all  fertile  soils,  and  from  the  soil  they  pass 

1  The  Latin  name  of  potassium  is  Kalium,  and  the  symbol,  K,  is 
taken  from  this. 

195 


196  THE    POTASSIUllf    GROUP. 

into  the  bodies  of  plants.  In  some  places  potassium  nitrate 
is  found  in  the  earth  in  large  quantities ;  this  is  true  of 
the  dry  tropical  countries  like  Egypt  and  India.  It  is 
very  soluble,  and  can  be  easily  washed  out  by  water.  It 
is  known  in  commerce  as  nitre  or  saltpetre.  Potassium 
compounds  are  obtained  for  commerce  either  from  plants 
or  from  the  soils  which  contain  them  in  large  enough 
quantities. 

Potassium  Carbonate.  K2  C  O3 . — When  wood  is  burned 
the  compounds  of  potassium  in  it  are  all  changed  to  potas- 
sium carbonate,  which  becomes  a  part  of  the  ash.  To  get 
it  out,  the  ashes  are  washed  with  hot  water,  for  it  is  well 
known  that  the  carbonate  is  soluble,  and  then,  to  get  it 
in  solid  form,  the  solution  is  evaporated  until  the  car- 
bonate crystallizes  out.  Of  course  everything  else  in  the 
ashes,  which  is  soluble,  will  conie  out  with  the  carbonate. 
The  product  is  very  impure ;  it  is  called  potash. 

The  only  chemical  action  in  this  process  is  the  burning 
of  the  wood.  The  method  of  getting  the  potash  out  of 
the  ashes  may  always  be  used  to  separate  a  substance 
which  is  soluble  when  it  is  mixed  with  others  which  are 
not. 

Many  of  the  other  useful  compounds  of  potassium  are 
made  from  the  carbonate  by  chemical  processes. 

Potassium  Hydroxide.  K  H  O.  — Potassium  will  drive 
the  metal  calcium  out  of  combination  with  hydrogen  and 
oxygen,  and  take  its  place.  This  fact  being  known,  the 
chemist  uses  it  to  get  potassium  hydroxide. 

He  mixes  slaked  lime,  Ca"H2O2,  with  potassium  car- 
bonate in  water,  and  boils  the  mixture.  The  metals  simply 
change  places. 

Ca"H202      +      K'2C03      =      CaC08      +     2KHO 

Calcium  Potassium  Calcium  Potassium 

with  become.  and 

Hydroxide  Carbonate  Carbonate  Hydroxide 


THE    POTASSIUM    GROUP.  197 

The  calcium  carbonate  is  a  white  solid  which  falls  to 
the  bottom,  while  the  potassium  hydroxide  stays  in  solu- 
tion. This  liquid  is  then  boiled  down  in  iron  pans. 

Potassium  hydroxide  is  the  same  as  caustic  potash.  It 
has  a  remarkable  attraction  for  water.  It  cannot  be  kept 
except  in  tight  bottles,  for  if  left  in  the  open  air  it  will 
take  moisture  enough  to  completely  dissolve  it.  Some 
other  things  have  this  same  property;  they  dissolve  in 
water  which  they  get  out  of  the  air.  Such  substances  are 
said  to  be  deliquescent. 

Other  Compounds  made  from  K2CO3.  —  There  are 
a  great  many  compounds  of  potassium  which  can  be  made 
by  starting  with  the  K2  C  03 . 

Ex.  126.  —  Make  a  little  potassium  chloride.  To  do  this, 
first  dissolve  K2C03,  as  much  as  you  can,  in  say  50  cc.  of 
water.  Then  add  H  Cl  slowly,  until,  after  shaking  it,  the 
liquid  will  redden  a  bit  of  blue  litmus-paper.  Finally 
evaporate  the  liquid  to  a  small  bulk  and  let  it  cool.  Pour 
the  liquid  away  from  the  crystals,  and  dry  them  on  filter- 
paper.  Keep  this  potassium  chloride,  K  Cl. 

Why  was  the  litmus-paper  used  ? 

What  reaction  took  place  ? 

Ex.  127.  —  Make  some  potassium  nitrate  in  the  same 
way,  only  use  nitric  instead  of  hydrochloric  acid.  If  the 
evaporation  is  carried  far  enough,  you  can  watch  the  crys- 
tals growing  in  the  liquid  while  it  cools.  Keep  this  KN03. 

Ex.  128.  —  Make  a  little  acid  potassium  tartrate.  To  do 
this  first  make  a  strong  solution  of  K2  C  03  in  one  tube  or 
bottle,  and  a  strong  solution  of  tartaric  acid  in  another. 
Then  add  the  acid  to  the  carbonate,  until  a  piece  of  litmus- 
paper  is  reddened  by  the  mixture.  A  white  crystalline 
precipitate,  or  solid,  will  be  made.  This  is  the  acid  potas- 
sium tartrate,  known  in  the  shops  as  "cream  of  tartar." 
Keep  this. 


198  THE   POTASSIUM    GROUP. 

When  the  two  liquids  were  put  together  in  the  last 
experiment  a  solid  made  its  appearance.  Any  solid  made 
in  this  way  is  called  a  precipitate.  It  takes  the  solid  form 
because  it  is  not  soluble  in  the  liquids.  This,  and  one  or 
two  others,  are  the  only  precipitates  which  we  can  make 
from  potassium  compounds,  because  the  acid  tartrate  and 
one  or  two  others  are  the  only  potassium  compounds  which 
do  not  readily  dissolve.  Even  these  dissolve  a  little,  and 
on  this  account  no  precipitate  will  come  unless  the  solu- 
tions used  are  strong. 

Flame  Color.  —  The  flame  of  potassium  is  violet,  and 
this  color  is  seen  when  any  compound  of  this  metal  is  de- 
composed by  heat.  Thus : 

Ex.  129.  —  I  take  a  piece  of  platinum-wire  and  bend  one 
end  into  a  round  loop  about  as  large 
as  this  O-  I  moisten  this  loop  and 
plunge  it  into  the  K  Cl  made  in  Ex. 
126.  A  little  of  the  salt  will  cling 
to  the  wire,  and  I  hold  it  in  the 
mantle  of  a  colorless  flame  (Fig. 
63),  and  notice  the  violet  color  of 
F1«-  *3-  '  the  flame  above. 

Look  at  this  colored  flame  through  a  piece  of  cobalt-blue 
glass.  Is  the  violet  visible  ? 

Ex.  130.  —  Thoroughly  clean  the  loop  so  that  it  will  not 
color  the  flame,  and  then  try  the  K  N  Os  of  Ex.  127  in  the 
same  way. 

Try  also  the  acid  tartrate  of  Ex.  128. 

The  color  will  sometimes  come  more  surely  if  the  loop 
is  moistened  with  hydrochloric  acid.  Try  K2  C  03  without 
hydrochloric  acid  and  then  with  it. 

None  but  potassium  compounds  will  give  this  color. 


THE    POTASSIUM    GROUP.  199 


SODIUM.    Na. 

The  metal  sodium  is  so  much  like  potassium  that  a 
separate  description  is  scarcely  needed.  Moreover,  the 
student  has  already  seen  or  handled  it  in  several  experi- 
ments of  this  course,  and  can  remember  its  appearance 
and  actions. 

Sodium  in  Nature Common  salt  is  made  of  sodium 

and  chlorine,  it  is  sodium  chloride,  Na  Cl.  Immense  quan- 
tities of  this  are  in  the  seas,  and  large  beds  of  it  are  found 
in  the  earth.  It  is  also  in  the  salt-springs  which  are  found 
here  and  there.  Many  other  compounds  of  sodium  also 
occur,  in  large*  quantities,  in  the  earth ;  the  carbonate  and 
the  nitrate  may  be  mentioned. 

Sodium  Carbonate.  Na2CO3.  —  This,  next  to  com- 
mon salt,  is  the  most  important  compound  of  the  metal. 
It  may  be  made  from  the  ashes  of  sea-plants,  just  as 
K2C03  is  made  from  the  ashes  of  land-plants,  but  enough 
of  it  could  not  be  had  from  this  source,  for  it  is  used  in 
making  glass,  and  soap,  and  in  other  large  industries. 

For  these  uses  it  is  made  from  common  salt.  About 
half  a  ton  of  salt  is  heated  in  a  furnace  with  sulphuric 
acid.  This  changes  the  salt  into  sodium  sulphate  and  sets 
hydrochloric  acid  free.  Thus  : 

H2SO4    +    2XaCl    =     Xa2SO4    +    211  Cl 

Then  this  sulphate,  Na2S04,  also  called  "salt-cake," 
is  mixed  with  coal  and  fragments  of  limestone,  and  heated 
intensely  until  the  whole  is  melted. 

The  sulphate  is  decomposed  by  the  carbon,  which  seizes 
its  oxygen  and  flies  away  as  carbon  monoxide  gas,  while 
sodium  sulphide  is  left  behind.  Thus  : 

Na2SO4    +    40    =    NaaS    +    4CO 


200  THE    POTASSIUM    GROUP. 

The  sodium  sulphide,  Na,j  S,  and  the  limestone,  Ca  C  03, 
then  attack  and  decompose  each  other, — 

NaaS    +     CaCO3     =     Na2CO3    +     CaS 

and  a  mixture  of  sodium  carbonate  and  calcium  sulphide, 
NagCOg  and  CaS,  called  "black-ash,"  is  left. 

The  carbonate  is  then  dissolved  out  of  the  black-ash 
by  water,  after  which,  by  evaporating  the  water,  the  car- 
bonate comes  out  as  crystals.  The  sodium  carbonate  made 
in  this  way  is  known  in  commerce  as  soda-ash. 

There  is  another  carbonate  of  soda  which  is  made  by 
running  carbon  dioxide  through  a  solution  of  NasCCV  it 
is  the  acid  carbonate,  NaHC03.  This  is  "baking-soda."1 
It  is  much  used  in  "baking-powders,"  and  to  furnish  the 
carbon  dioxide  gas  for  making  "soda-water." 

Sodium  Hydroxide.  NaHO.  —  This  substance  is  so 
much  like  potassium  hydroxide  that  either  may  be  used 
for  the  same  purposes  in  the  laboratory  and  in  the  arts. 
Both  are  used  in  soap-making.  They  combine  with  the 
acids  which  are  in  fats  and  oils,  and  the  salts  which  are 
thus  made  are  called  soaps.  There  is  this  difference, 
however:  the  potassium  hydroxide  makes  the  soft  soaps, 
while  the  sodium  hydroxide  yields  the  hard  soaps. 

The  "  caustic  soda,"  or  sodium  hydroxide,  is  made  from 
Nag  C  03  in  the  same  way  (how  ?)  that  "  caustic  potash  "  is 
made  from  K2CO3. 

The  compounds  of  sodium  are  all  quite  freely  soluble 
in  water.  (Can  a  precipitate  be  obtained  from  a  solution 
of  any  of  them  by  tartaric  acid,  as  in  Ex.  128?) 

1  In  the  exercises,  pp.  39  and  40,  the  student  must  have  come  to 
the  conclusion  that  "  baking-soda"  is  a  sodium  carbonate.  Having 
now  gathered  more  facts,  he  finds  that  his  conclusion  was  true,  but  that 
it  was  not  the  whole  truth.  Wholly  reliable  conclusions  can  never  be 
reached  until  "  the  facts  are  all  in."  •;.. 


THE   POTASSIUM    GROUP.  201 

Flame  Color.  —  The  flame  of  sodium  is  pure  yellow, 
and  any  of  its  compounds  decomposed,  by  heat,  will  yield 
this  color  intensely.  Thus  : 

Ex.  131.  —  Wash  the  platinum  loop  and  hold  it  in  the 
Bunsen  flame.  Is  not  the  flame  tinged  yellow?  Wash 
the  wire,  and  burn  it  repeatedly  until  it  does  not  give  the 
yellow  tint,  and  then  use  any  sodium  compound.  Note 
the  rich  color  it  imparts. 

Look  at  this  colored  flame  through  cobalt-blue  glass : 
is  the  yellow  color  to  be  seen  ? 

There  is  a  little  sodium  in  the  air,  in  the  dust  of  the 
room,  and  almost  everywhere.  The  yellow  tint  of  sodium 
may  be  given  by  this  small  quantity  that  is  ever  present. 
Only  a  deep,  rich  yellow  can  be  trusted  to  show  the  pres- 
ence of  a  sodium  salt  in  quantity. 

Ex.  132.  —  Make  a  mixture  of  a  sodium  and  a  potassium 
salt  and  burn  the  mixture  on  the  platinum  loop. 

Which  color,  yellow  or  violet,  can  you  get  with  the 
naked  eye  ? 

Which,  if  you  look  through  cobalt  glass  ? 

Ex.  133.  —  Make  a  strong  solution  of  some  of  the  mix- 
ture, and  then  add  a  little  tartaric  acid.  Does  a  precipi- 
tate form  in  the  liquid  ?  Is  this  precipitate  made  by  the 
potassium  or  the  sodium  salt  ?  What  is  it  ? 

AMMONIUM  (?)    NH4. 

We  have  seen  that  from  ammonia,  NH3,  we  may  get 
a  class  of  salts  called  the  ammonium  salts.  Is  there  a 
metal  in  these  salts  ? 

Some  Facts Ammonia,  NH3,  is  very  soluble  in 

water  (Ex.  56),  and  this  solution  will  restore  reddened 
litmus  to  blue,  and  it  also  neutralizes  acids.  This  shows 


202  THE    POTASSIUM    GROUP. 

that  it  is  a  base,  and   yet   it  is  made   up  of  nothing  but 
nitrogen,  hydrogen,  and   oxygen,  —  all  non-metals,  — 

NH8  +  H2O  =  NH4HO. 

Ammonia  combines  with  hydrochloric  acid  (Ex.  0),  to 
make  what  is  called  ammonium  chloride.  This  is  a  white 
solid,  which  has  all  the  properties  of  a  salt,  resembling  the 
chlorides  of  sodium  and  potassium,  and  yet  it  is  made  up 
of  nothing  but  nitrogen,  hydrogen  and  chlorine,  —  all  non- 
metals. 

Ammonia  solution  neutralizes  nitric  acid  and  forms  am- 
monium nitrate  (Ex.  59),  and  this  is  as  much  a  salt  as 
is  any  other  nitrate,  but  yet  it  is  made  of  only  nitrogen, 
hydrogen,  and  oxygen, — all  non-metals.  We  find  no  metal 
in  these  ammonium  compounds. 

Comparison  of  Formulas. — Let  us  now  compare  these 
compounds  with  those  which  do  contain  a  metal, — say  the 
metal  potassium. 

Potassium  hydrate,  K  H  O,   and  Ammonium  hydrate,  N  H4  H  O 
Potassium  chloride,  K  Cl,       and  Ammonium  chloride,  N  II4  Cl 
Potassium  nitrate,    K  N  O8,  and  Ammonium  nitrate,    N  H4  X  Os 

Notice  that  instead  of  K  in  the  potassium  compounds 
we  find  N  H4  in  the  ammonium  compounds.  The  N  H4 
acts  just  like  the  metal  potassium  in  making  salts,  and 
this  leads  us  to  say  that  N  H4  may  be  a  metal  also. 

A  HYPOTHETICAL  METAL.  —  But  we  cannot  get  the  NH4 
separate,  as  a  metal.  These  atoms  hang  together  well 
while  in  the  salts,  and  in  reactions,  but  part  at  once  if 
driven  out  together.  In  chemical  changes  the  group  acts 
as  if  it  were  a  metal,  and  we  may  suppose  it  to  be  one. 
We  call  it  ammonium,  and  may  give  it  a  symbol,  Am. 

Its  Salts.  —  The  ammonium  salts  are  numerous.  Am- 
uiouium  chloride,  Am  Cl,  Ammonium  carbonate,  Am4C  O3, 


THE    POTASSIUM    GROUP.  203 

and  ammonium  sulphide,  Am2  S,  may  be  mentioned.  The 
source  of  these  salts  in  commerce  has  been  already  given, 
and  should  now  be  recalled  by  the  student,  p.  85. 

THE  SULPHIDES.  —  Only  the  sulphides  need  a  word  more. 
There  is  more  than  one  ammonium  sulphide,  but  they  are 
all  made  by  dissolving  hydrogen  sulphide  gas  in  ammonia 
water.  Large  volumes  of  gas  will  be  absorbed.  Thus : 

H2  S  +  N  H3  =  N  H4  H  S,  —  Ammonium  hydrosulphide. 

But  if  ammonia  is  also  present  with  this  N  H4  H  S,  they 
combine.  Thus : 

N  H4  H  S  +  N  H8  =  (N  H4)2  S,  —  Ammonium  sulphide. 

The  solution  of  these  two  sulphides  is  colorless,  but  if 
any  free  sulphur  is  in  it,  the  liquid  becomes  yellow.  The 
sulphur  unites  with  the  sulphide.  Thus: 

(N  H4)2  S  +  S  =  (N  H4)2  S2,  —  Ammonium  disulphide. 

This  last-named  suljjhide  is  yellow. 

The  ammonium  sulphide  solution  is  one  of  the  most 
useful  reagents,  as  the  student  will  soon  find.  But  this  re- 
agent, called  ammonium  sulphide,  is  not  a  single  compound  ; 
it  is  a  mixture  of  all  these.  We  may  study  the  ammonium 
compounds  further,  and  compare  them  with  potassium  and 
sodium,  as  follows  : 

Ex.  134.  —  Add  some  tartaric  acid  solution  to  a  strong 
solution  of  any  ammonium  salt. 

Note  whether  a  precipitate  comes  as  with  potassium. 

Ex.  135.  —  Find  out  whether  an  ammonium  salt  will 
give  any  particular  flame-color. 

Ex.  136.  —  Mix  a  little  solid  or  liquid  ammonium  salt, 
of  some  kind,  with  a  little  K  H  0,  and  gently  heat  it  in  a 
test-tube. 

Notice  the  odor ;  what  substance  is  set  free  ? 


204  THE   POTASSIUM    GROUP. 

Ex.  137.  —  Place  a  little  solid  ammonium  salt  in  a  por- 
celain dish,  and  gradually  heat  it. 

Does  it  melt  ?     What  change  does  occur  ? 

THE  FACTS.  —  Tartaric  acid  gives  a  white  precipitate  in 
strong  solutions  of  ammonium  salts,  because  the  acid  tar- 
trate  of  ammonium  is  not  very  soluble.  But  the  ammo- 
nium salts  generally  are  very  soluble,  and  on  this  account 
they  need  not  be  expected  to  give  precipitates.  They  give 
no  color  to  the  flame.  They  are  decomposed  when  heated 
with  caustic  potash,  and  then  yield  ammonia  gas,  known 
by  its  odor.  Heat  alone  drives  them  into  vapor  completely, 
leaving  nothing  behind. 

The  change  of  a  solid  directly  to  vapor,  without  first 
melting,  is  called  sublimation.  Camphor  is  the  most  fa- 
miliar example  of  substances  which  sublime  when  heated. 
The  ammonium  salts,  as  a  class,  do  this. 

THE    POTASSIUM    GROUP. 

Potassium,  sodium,  and  ammonium  (?)  are  very  much 
alike,  and  besides  these  there  are  three  other  metals, 
whose  salts  are  less  common  and  useful,  also  like  these 
in  chemical  character.  They  are  lithium,  caesium,  and 
rubidium.  These  six  form  a  single  family  of  metals, 
generally  called  the  Metals  of  the  Alkalies. 

These  elements  are  all  soft,  light,  and  silvery  white. 
They  lose  their  luster  at  once  in  air,  because  they  have 
so  strong  attraction  for  oxygen  that  the  surface  is  tar- 
nished with  oxide.  They  cannot,  therefore,  be  kept  in  air, 
but  must  be  put  up  in  naphtha,  a  liquid  which  has  no 
oxygen  in  it.  They  decompose  water  whenever  they  touch 
it,  and  form  bases  by  the  action. 

These  are  the  most  powerful  bases  known, — the  most 
caustic  and  the  most  ready  to  neutralize  acids.  They 


THE    POTASSIUM    GROUP.  205 

form  the  same  classes  of  salts,  and  these  salts  are  much 
alike  in  properties.     These  metals  are  all  univalent. 

QUERY.  —  By  what  experiments  would  you  find  out  whether 
a  given  salt  is  a  potassium,  a  sodium,  or  an  ammonium  com- 
pound? 

APPLICATION.  —  Take  from  the  teacher,  or  a  friend  who  knows 
what  they  are,  some  substances,  and  see  if  you  can  decide 
whether  each  is  a  potassium,  or  a  sodium,  or  an  ammonium  com- 
pound. 


THE    CALCIUM    GROUP. 

CALCIUM.    Ca". 

THE  metal  calcium  is  about  as  hard  as  gold,  and  shines 
with  a  yellow  luster.  It  tarnishes  quickly  in  air.  No 
use  has  ever  been  made  of  the  element  itself,  but  its 
compounds  are  not  only  very  useful,  but  very  abundant. 

Occurrence  in  Nature Calcium  carbonate,  Ca"C03, 

is  one  of  the  largest  constituents  of  the  earth.  Marble  is 
its  purest  natural  form,  but  limestone  is  chiefly  the  same 
thing,  and  the  limestone  rocks  make  up  a  large  part  of 
the  earth's  crust.  Calcium  carbonate  is  the  starting-point 
in  the  manufacture  of  the  useful  salts  of  this  metal. 

The  Effect  of  Heat  on  the  Carbonate When  a  piece 

of  marble  is  heated  intensely,  it  will  not  be  much  changed 
in  looks;  its  size  will  be  the  same,  its  color  somewhat 
whiter.  But  it  will  be  found  to  be  more  easily  crushed, 
and  it  is  easily  shown  that  a  chemical  change  has  occurred. 
This  may  be  done  by  treating  it  with  water.  Very  soon 
after  being  wetted,  the  stone  begins  to  swell  and  crack  and 
crumble,  while  volumes  of  steam  arise,  and  when  all  is  over 
a  fine  white  powder  remains. 

The  fact  is,  that  heat  decomposes  the  marble,  and  drives 
off  carbon  dioxide.  Thus : 

CaC<)3  +  heat  =  CaO  4-  C  O2 

and  the  white  mass  left  behind  is  the  calcium  oxide,  Ca  O. 
The  common  name  of  this  oxide  is  quick-lime. 

By  this  simple  chemical  process  large  quantities  of 
quick-lime  are  manufactured.  The  furnaces  are  *  called 
lime-kilns. 

206 


THE    CALCIUM    GROUP.  207 

The  white  powder  made  by  the  action  of  water  on 
quick-lime  is  called  slaked-lime.  The  water  actually  com- 
bines with  the  oxide.  Thus  : 

CaO  +  H2O  =  CaH2O2  +  heat 

We  see  by  the  formula  that  slaked  lime  is  calcium 
hydroxide.  The  heat  of  this  chemical  action  is  remarkable. 

Among  many  uses  of  slaked-lime,  we  may  mention  that 
of  making  mortar  for  building  purposes.  Mortar  is  made 
by  mixing  slaked-lime  and  sand,  and  it  is  used  to  cement 
together  the  bricks  or  stones  in  the  walls  of  buildings. 
Fresh  mortar  is  very  weak;  it  becomes  a  strong  cement 
after  it  is  laid  up  in  the  walls.  The  chemistry  of  the 
change  is  this  : 

Calcium  hydroxide  absorbs  the  carbon  dioxide  of  the  air, 
when  exposed,  and  is  slowly  changed  by  it  into  calcium 
carbonate,  which  is  hard  and  stony,  and  this,  filled  in  with 
grains  of  sand,  becomes  a  strong  and  solid  mass  which 
cements  the  bricks  or  stones  together. 

The  calcium  hydroxide,  CaH2O2,  is  slightly  soluble  in 
water:  the  solution  is  known  as  lime-water,  and  is  very 
useful  to  the  chemist  (Exs.  6,  26,  73),  and  to  some  extent 
in  medicine. 

Effect  of  Acids  on  the  Carbonate Even  the  weaker 

acids  will  decompose  marble,  and  in  fact  most  other  car- 
bonates. Water  and  carbon  dioxide  are  produced  by  this 
action  and  the  escape  of  this  last  in  bubbles  is  the  effer- 
vescence which  always  occurs.  Turn  back,  now,  to  the 
preparation  of  carbon  dioxide  (Ex.  73).  We  wanted  the 
C02  then,  and  did  not  take  account  of  anything  else.  But 
we  can  now  see  what  the  complete  reaction  really  was. 
Thus  :  — 

Ca"CO3  +  2IIC1  became  CaCl2  +  H2O  +  CO2 


208  THE    CALCIUM    GROUP. 

and  this  illustrates  the  action  of  other  acids  on  this  sub- 
stance. Carbon  dioxide,  water,  and  a  salt  of  calcium  are 
the  products. 

Effect  of  Water  on  the  Carbonate Pure  water  will 

not  dissolve  this  carbonate,  but  water  holding  CO2  in 
solution  dissolves  it  quite  readily.  Let  the  C  O2  escape, 
or  drive  it  out  by  heat,  and  the  carbonate  reappears. 

This  action  goes  on  in  nature.  Rain-water  contains 
C  O2,  taken  from  the  air,  and  as  this  water  runs  over  the 
lime-rocks  it  dissolves  and  carries  some  of  their  substance 
along.  But  when  this  solution  is  exposed  to  air,  the  C  O2 
escapes,  and  the  water  then  drops  the  solid  carbonate. 
This  occurs  in  caverns  where  the  water  trickles  through 
their  roofs.  Each  drop  leaves  a  little  solid  carbonate 
behind  when  it  falls,  and  an  icicle-like  mass  slowly  grows 
from  the  roof.  This  is  called  a  stalactite.  Another  grows 
up  from  the  floor,  this  is  called  a  stalagmite. 

The  Sulphate.  CaSO4  4-  2H2O.  — This  is  known  as 
gypsum,  —  a  crystalline  mineral  found  in  some  abundance, 
and,  when  ground  to  powder,  quite  useful  as  a  fertilizer. 
This  mineral  gives  up  its  water,  2  H2  O,  when  strongly 
heated,  and  crumbles  to  a  fine  white  powder  called  "  Plas- 
ter of  Paris."  Wet  this  plaster  of  Paris,  and  it  combines 
with  water  again  and  hardens  into  stone.  This  curious 
property  makes  the  sulphate  useful  for  making  casts. 

Glass  contains  calcium  silicate,  combined  with  silicates 
of  sodium  or  potassium  (see  p.  185),  and  bleaching  powder  is 
a  mixture  of  calcium  hypochlorite  and  calcium  chloride. 
How  is  it  prepared  ?  See  p.  141,  and  Ex.  86. 

To  Prepare-  the  Insoluble  Compounds.  —  Among  the 
many  salts  of  calcium  there  are  several  that  are  not  solu- 
ble in  water,  especially  in  water  that  contains  ammonia, 
and  such  can  be  obtained  by  precipitation. 

JKr.  138.  —  Place  about  5  cc.  of  calcium  chloride  in  a  test- 


THE    CALCIUM    GROUP.  209 

tube,  add  about  as  much  water,  and  heat  the  mixture  up  to 
boiling-point.  Then  add  slowly  a  solution  of  ammonium 
carbonate  as  long  as  it  continues  to  produce  the  precipitate. 
The  time  to  stop  may  be  known  by  letting  the  solid  settle 
a  little,  and  then  notice  whether  another  drop  of  the  ammo- 
nium carbonate  has  any  effect.  The  white  precipitate  is 
calcium  carbonate.  Am  Cl  was  also  made,  but  stays  dis- 
solved in  the  clear  liquid.  Thus : 

CaCl2  +  (NH4)2CO3  =  CaCO3  +  2NH4C1 

A  very  valuable  fact  is  shown  in  this  experiment.  Notice 
that  one  carbonate  precipitates  another.  We  wanted  to 
make  the  insoluble  CaCO3,  and  we  did  it  by  using  the  sol- 
uble (N  H4)2  C  03 .  The  fact  is,  that  a  soluble  salt  precipi- 
tates an  insoluble  salt  of  the  same  class  as  itself.  If  we 
want  an  insoluble  hydrate  we  will  use  some  soluble  hydrate 
to  make  it.  Or,  if  we  want  an  insoluble  sulphide  we  will 
use  some  soluble  sulphide  to  produce  it.  There  are  a  few 
exceptions  to  this  rule,  but  it  is  so  generally  true  as  to 
be  an  excellent  guide. 

For  example,  we  wish  to  make  the  insoluble  calcium 
sulphate.  Let  us  select  some  soluble  sulphate  to  do  it 
with.  It  may  be  potassium  sulphate,  K2S04,  or  hydrogen 
sulphate,  H2  S  O4 ,  or  some  other. 

Ex.  139. — Place  about  5  cc.  of  water  in  a  test-tube,  and 
add  about  as  much  solution  of  any  soluble  compound  of 
calcium,  —  such  as  the  chloride  or  nitrate,  —  and  then  add, 
little  by  little,  a  solution  of  K2S04. 

Repeat  the  operation,  using  H2S04. 

The  precipitate  is  calcium  sulphate  in  both  cases. 

Can  you  write  the  reactions  ? 

But  the  term  insoluble  is  not  applied  to  a  substance, 
because  the  fluid  dissolves  absolutely  none  of  it;  we  call 
a  thing  insoluble  when  a  fluid  dissolves  only  very  little. 


210  THE    CALCIUM    (UIOUP. 

Everything  is  soluble  in  some  degree,  but  in  many  cases 
the  quantity,  which  will  dissolve  in  the  amount  of  fluid 
used,  is  too  small  to  be  taken  account  of.  Such  are  called 
insoluble  substances. 

Now  CaS04  is  somewhat  soluble  in  water.  In  fact, 
400  cc.  of  water  will  dissolve  about  1  g.  of  it,  and  if  you 
have,  say  10  cc.  of  fluid  in  your  test-tube  (Ex.  139),  there 
must  be  about  ,10  of  a  gram  of  the  sulphate  in  solution ; 
the  rest  of  the  sulphate  is  the  precipitate.  A  precipitate 
will  always  be  seen  whenever  the  fluid  present  cannot 
dissolve  all  of  the  substance  which  the  reagent  makes, 
but  not  otherwise. 

To  Prepare  Soluble  Compounds If,  in  any  case, 

the  new  compound  made  by  a  chemical  reagent  is  soluble, 
it  may  be  obtained  by  evaporating  the  clear  liquid,  in 
which  it  is  dissolved,  until  crystals  will  form,  or  to  dry- 
ness  if  necessary.  For  practice,  the  student  should  pre- 
pare some  calcium  nitrate,  and  calcium  acetate,  from  the 
pure  carbonate,  or  from  marble. 

THE    CALCIUM    GROUP. 

Two  other  metals,  barium,  Ba",  and  strontium,  Sr",  are 
very  much  like  calcium,  and  these  three  form  the  calcium 
group  of  metals,  or,  as  it  is  also  called,  the  group  of  the 
alkaline  earths. 

In  general,  these  three  metals  combine  with  the  same 
substances  and  in  the  same  proportions.  Their  attraction 
for  oxygen  makes  them  tarnish  quickly  in  air,  and  en- 
ables them  to  decompose  water  when  they  touch  it.  The 
hydroxides  thus  formed  are  strongly  alkaline.  In  these 
chemical  actions  barium  is  more  energetic  than  strontium, 
and  strontium  more  than  calcium.  Now  this  is  also  the 
order  of  their  atomic  weights,  if  we  start  with  the  largest. 

Thus: 

Ba  =  137  Sr  =  87:5  Ca  =  40 


THE    CALCIUM    GROUP.  211 

This  is  another  illustration  of  the  curious  fact,  noticed 
among  groups  of  the  non-metals,  that  the  properties  of 
elements  seem  to  depend  on  their  atomic  weights. 

The  great  resemblance  of  barium  and  strontium  to  cal- 
cium will  be  seen  if  we  make  and  compare  some  salts  of 
these  three  metals.  Some  differences  will  also  be  dis- 
covered. 

Ex.  140.  —  Make  the  carbonates  of  barium  and  strontium 
just  as  that  of  calcium  was  made  in  Ex.  138,  and  notice 
how  much  alike  these  three  carbonates  appear. 

Ex.  141-  —  Arrange  three  test-tubes,  each  with  5  cc.  of 
water,  and  add  to  one  5  cc.  of  strong  solution  of  Ba  C12 ,  to 
the  second,  as  much  strong  solution  of  SrCl2,  and  to  the 
third,  as  much  strong  solution  of  CaCl2.  Then  add  to  each 
a  little  solution  of  calcium  sulphate. 

Notice  a  precipitate  at  once  in  the  Ba  tube  only.  Heat 
the  other  two  to  boiling,  and  notice  then  a  precipitate  in 
the  Sr  tube,  but  none  in  the  other. 

The  barium  sulphate  forms  at  once  in  the  cold. 

The  strontium  sulphate  at  once  only  when  heated. 

The  calcium  sulphate  does  not  form  at  all. 

This  experiment  will  help  us  to  decide,  in  any  case, 
which  one  of  these  three  metals,  if  either,  is  present  in  a 
given  solution.  But  why  is  not  the  calcium  sulphate  pre- 
cipitated here  as  it  was  in  experiment  139  ? 

Flame  Colors.  Ex.  142.  —  A  volatile  compound  of  cal- 
cium will  tinge  the  flame  yellow-red  ;  of  strontium,  brilliant 
crimson ;  of  barium,  green.  Try  these  compounds,  and  ob- 
serve the  flames  with  the  naked  eye,  and  also  through  cobalt 
glass.  Mark  well  the  difference  between  these  and  the 
flame  colors  of  potassium  and  sodium. 


METALS    OF    THE    ZINC    GROUP. 

Magnesium.  Mg".  —  The  metal  magnesium  is  found 
as  a  carbonate  and  as  a  silicate,  these  two  being  its  most 
important  compounds  in  the  rocks.  Its  sulphate,  known 
as  Epsom  salt,  is  its  most  important  compound.  It  is 
found  in  solution,  and  in  some  mineral  springs  it  is  a  val- 
uable constituent.  What  is  commonly  called  magnesia  is 
the  oxide  of  this  metal,  Mg"O.  It  is  used  in  medicine. 
The  Epsom  salt,  Mg  S  O4  +  7  H2  0,  is  still  more  valuable 
as  a  medicine  ;  but  on  the  whole  magnesium  and  its  com- 
pounds do  not  rank  high  among  useful  substances. 

The  chemical  actions  of  magnesium  compounds  are  a 
little  like  those  of  the  calcium  group.  Its  carbonate  is 
insoluble  in  water. 

Ex.  143.  —  Precipitate  Mg"CO2  from  its  chloride  just 
as  was  done  for  CaCO3  in  Ex.  138. 


Ex.  144-  —  Put  5  cc.  ammonium  chloride  in  a  test-tube, 
and  to  this  add  5  cc.  of  magnesium  chloride.  Then  add 
the  ammonium  carbonate.  Does  a  precipitate  form?  If 
not  it  shows  that  magnesium  carbonate  is  soluble  in 
ammonium  chloride.  This  is  a  fact.  In  this  respect  this 
carbonate  differs  from  those  of  the  calcium  group.  In 
general  the  compounds  of  this  metal  are  more  soluble  than 
those  of  that  group. 

ZINC.    Zn". 

The  metal  zinc  is  found  in  several  minerals  which  occur 

in  considerable  quantities  in  the  rocks,  such  as  "  calamine," 

which  is  the  carbonate,  "blende,"  which  is  the  sulphide, 

and  "  zincite",  the  oxide.     These  are  its  most  valuable  ores. 

212  • 


METALS    OF    THE    ZINC    GROUP.  213 

Zinc  is  a  useful  metal,  and  it  is  manufactured  on  a  largo 
scale  from   these  native  compounds. 

Manufacture  of  Zinc.  —  Suppose  the  metal  is  to  be 
taken  out  of  the  oxide,  Zn  0.  The  problem  is  how  to  get 
rid  of  the  oxygen.  Turn  back  to  Ex.  72,  and  you  recall 
the  strong  attraction  of  carbon  for  oxygen,  and  how,  on  this 
account,  carbon  reduced  Cu  0  to  metallic  copper.  Now  this 
is  the  fact  applied  to  get  the  zinc  out  of  Zn  0  on  a  large 
scale.  The  oxide  and  charcoal  are  put  into  vessels  of  fire- 
clay and  heated  in  a  furnace.  What  reaction  occurs  ?  It 
may  be  written : 

Zn  O  +  C  =  C  O  +  Zn. 

The  zinc,  in  the  form  of  vapor,  is  led  out  into  cold 
vessels,  where  it  is  condensed. 

But  suppose  the  zinc  is  to  be  taken  out  of  one  of  the 
other  ores, —  say  the  sulphide,  Zn  S.  The  problem,  then,  is 
to  get  rid  of  the  sulphur.  The  problem  is  solved  by  first 
changing  the  sulphide  into  the  oxide,  and  then  reducing 
the  oxide  by  carbon  as  before.  And  to  change  the  sul- 
phide to  oxide  it  is  simply  heated  in  the  air,  when  oxygen 
of  the  air  takes  the  place  of  sulphur  in  the  ore.  Thus : 

Zn  S  +  3  O  =  Zn  O  +  S  O2 

This  heating  of  an  ore  in  the  air  is  called  roasting.  The 
object  of  it  is  to  change  the  ore  to  an  oxide.  It  is  in  many 
cases,  as  in  this  one,  the  first  step  in  the  process  of  get- 
ting a  metal  from  its  ores. 

Uses  of  Zinc.  —  The  uses  of  zinc  are  quite  numerous. 
When  heated  to  a  temperature  above  that  of  boiling  water 
(125° -150°)  it  can  be  rolled  out  into  thin  sheets.  This 
sheet-zinc  is  in  familiar  use.  Zinc  is  brittle,  and  cannot 
be  rolled  out  at  temperatures  much  higher  or  lower  than 
those  given  above.  Zinc  is  also  used  as  a  covering  for 


214  METALS    OF    THE    ZINC    GROUP. 

sheet-iron;  for  this  purpose  sheets  of  iron  are  simply 
dipped  in  melted  zinc;  it  is  then  called  galvanized  iron. 
Zinc  and  copper  melted  together  form  brass.  Zinc,  cop- 
per, and  nickel,  melted  together,  form  German  silver. 
Substances  like  these,  which  consist  of  two  or  more 
metals  together,  are  called  alloys.  These  and  other  alloys 
of  zinc  are  useful. 

Compounds  of  Zinc.  —  Of  the  compounds  of  zinc  we 
may  mention  the  following :  zinc  oxide,  which  is  used  as 
a  paint  under  the  name  of  zinc  -white,  and  is  made  for  this 
purpose  by  heating  the  carbonate.  Zinc  chloride,  used  by 
tinners  for  cleaning  the  surface  of  metals  for  soldering, 
and  also  as  a  disinfectant.  Zinc  sulphate,  known  as  white 
vitriol,  a  poisonous  substance,  but  used  in  small  quantities 
in  medicine. 

Preparation  of  Insoluble  Compounds.  —  Among  its 
compounds  which  are  insoluble  in  water  are  the  carbon- 
ate, the  sulphide,  and  the  hydroxide.  To  make  these  we 
may  start  with  zinc  chloride. 

Ex.  145.  —  Make  a  solution  of  zinc  chloride  for  use,  by 
putting  bits  of  zinc  in  a  bottle  and  pouring  a  few  cubic  cen- 
timeters of  H  Cl  on  them.  There  should  be  zinc  left  in 
the  bottle  when  the  action  is  over,  for  then  the  zinc  chlo- 
ride will  be  free  from  acid. 

Ex.  146.  —  Add  a  few  drops  of  this  solution  of   ZnCl2 
to  10  cc.  of  water,  and  then  add  (N  H4)2  C03. 
Describe  the  result  and  write  the  reaction. 

Ex.  147.  To  10  cc.  of  water,  with  a  few  drops  of  Zn  C12 
add  AnigS.1  What  is  the  white  precipitate  which  falls? 

1  This  ammonium  sulphide,  and  the  hydrogen  sulphide  for  the  next 
experiment,  are  made  by  passing  H2  S  through  dilute  ammonia  (half 
water)  for  one  and  water  for  the  other.  Use  the  same  apparatus  as 
in  Ex.  107. 


METALS    OF    THE    ZINC    GROUP.  215 

Write  the  reaction.  What  soluble  compound  is  also 
made  in  this  reaction? 

Ex.  148.  To  a  few  cubic  centimeters  of  Zn  C12  add  a  few 
drops  of  hydrochloric  acid,  and  then  add  a  solution  of 
hydrogen  sulphide,  H2S.  Do  you  get  a  precipitate?  If 
not,  it  shows  that  Zn  S  is  soluble  in  this  liquid. 

We  make  the  sulphide  whether  we  use  Am.,  S  or  H2S, 
but  the  first  is  an  alkaline  substance,  while  the  second  is 
an  acid,  and  we  find  that  the  sulphide  is  not  soluble  in 
the  alkaline  liquid,  Ex.  147,  while  it  is  soluble  in  the 
acid  liquid,  Ex.  148. 

Ex.  149.  —  To  a  few  cubic  centimeters  of  the  Zn  C12  with 
an  equal  bulk  of  water  add  N  H4  H  0  little  by  little,  until 
after  shaking  it,  and  then  blowing  the  air  out  of  the  tube, 
the  strong  odor  of  ammonia  remains. 

Describe  the  two  changes  which  occurred. 

The  explanation  is  this:  Ammonium  hydroxide  changes 
the  zinc  chloride  to  zinc  hydroxide,  which  takes  the  form 
of  a  white  precipitate  because  it  is  insoluble  in  water.  But 
it  is  soluble  in  ammonium  hydroxide,  and  so  just  as  soon  as 
there  was  added  more  than  enough  to  make  the  precipitate, 
the  excess  began  to  dissolve  that  which  had  been  made. 
Whenever,  as  in  this  case,  a  precipitate  dissolves  in  the 
reagent  which  makes  it,  it  is  said  to  be  soluble  in  excess. 

The  Zinc  Group Magnesium,  zinc,  and  cadmium  are 

the  members  of  this  group.  These  elements  are  much 
alike.  They  are  all  bluish-white  metals.  They  have 
many  of  the  same  properties,  but  in  different  degrees. 

For  example,  cadmium  melts-  at  a  comparatively  low 
temperature,  zinc  at  a  higher ;  423°  C.,  and  magnesium  at 
one  still  higher.  Cadmium  becomes  a  vapor  at  a  low  red 
heat,  zinc  if  heated  but  little  hotter,  and  magnesium  at 
a  bright  red  heat.  They  take  fire  in  the  air,  cadmium 


216  METALS    OF    THE    ZINC    GROUP. 

burns  less  freely,  zinc  with  a  fine  blue  flame,  and  magne- 
sium with  a  dazzling  whiteness.  They  decompose  dilute 
acids,  cadmium  rather  slowly,  zinc  more  freely,  and  mag- 
nesium very  promptly. 

This  order  of  their  properties  is  also  the  order  of  their 
atomic  weights,  beginning  with  the  largest.  Thus : 

Cd        Zn        Mg 
112        65         24 

SUGGESTION.  —  Compare,  by  experiment,  the  action  of  H2  S,  and 
of  Am2  S,  on  some  soluble  compounds  of  zinc,  cadmium,  and  mag- 
nesium, and  note  the  different  results. 

Then  take  from  the  teacher  or  a  friend,  who  knows  what  they 
are,  some  specimens,  and  see  if  you  can  decide  whether  each  is  a 
compound  of  either  of  these  metals. 


THE    IRON    GROUP, 

MANGANESE.    MR". 

As  a  metal,  manganese  need  not  detain  us,  since  it 
is  rarely  used  in  chemistry  or  the  arts.  In  the  form  of 
the  "black  oxide,"  MnOa,  it  is  found  in  many  parts  of  the 
earth.  This  is  its  chief  ore,  although  it  occurs  in  other 
minerals  and  rocks  in  some  abundance.  Jt  unites  with 
oxygen  in  several  proportions,  reminding  us,  in  this  re- 
spect, of  nitrogen:  there  are  five  oxides  of  each. 

Salts  of  Manganese.  -  -  Two  of  these  —  those  which 
contain  least  oxygen — act  with  acids  to  produce  salts: 
they  are  basic,  while  one  of  them  —  that  which  contains 
most  oxygen  —  acts  with  bases  to  produce  salts :  it  is  acid. 
The  other  two  do  not  produce  salts  at  all :  they  are  neu- 
tral. The  student  should  think  of  the  bearing  of  this  fact 
on  our  definition  of  metal,  p.  192. 

From  the  basic  oxide,  Mn  0,  we  may  get  manganous 
chloride  and  manganous  sulphate,  which  are  the  salts  most 
common  in  the  laboratory,  while  from  the  acid  oxide, 
Mn2O-,  we  may  get  the  potassium  permanganate,  which  is  a 
beautiful  salt,  much  used  in  the  laboratory  and  out  of  it. 
Its  solution  in  water  is  intensely  purple,  but  this  fine  color 
is  quickly  lost  in  presence  of  anything  which  has  an  affinity 
for  oxygen.  It  parts  with  its  oxygen  so  readily  to  other 
things,  that  it  is  a  most  powerful  oxidizing  agent.  In  the 
laboratory,  it  is  used  for  this  purpose,  and  out  of  it  too  ;  for, 
since  bad  odors  and  putrid  organic  matter  are  destroyed  by 
oxygen,  the  permanganate  is  a  valuable  disinfectant. 

PREPARATION  OF  SOME  INSOLUBLE  SALTS.  —  Among  the 
insoluble  salts  of  manganese  we  may  mention  the  niangan- 

.  217 


218  THE    IRON    GROUT. 

cms  carbonate,  sulphide,  and  hydrate.  A  study  of  these 
will  reveal  some  of  the  most  characteristic  reactions  of  this 
metal. 

Ex.  150. — To  make  the  carbonate,  proceed  exactly  as  in 
Ex.  146  with  zinc,  using  a  solution  of  manganous  sulphate 
instead  of  the  zinc  compound. 

What  is  the  color  of  manganous  carbonate  ? 

What  is  the  color  after  some  time  in  the  air  ? 

To  answer  this  last  question,  it  is  well  to  filter  the  liquid, 
and  leave  the  precipitate  on  the  filter.  The  change  you 
will  discover  is  caused  by  the  oxygen  of  air,  which  changes 
the  manganoMs  carbonate  to  the  mangan/c  hydrate.  This 
change  does  not  occur  in  the  case  of  zinc. 

Ex.  151.  —  To  make    the    sulphide,  proceed   just   as    in 
Ex.  147  with  zinc,  using  manganous  sulphate,  and  Am2  S. 
What  is  the  color  of  the  manganous  sulphide  ? 
Write  the  reaction  which  took  place. 
What  soluble  compound  is  made  at  the  same  time  ? 

Ex.  152.  —  Try  to   make   the   sulphide   by  using   H2S. 
Proceed  exactly  as  in  Ex.  148  with  zinc. 
What  is  the  result,  and  why  ? 

Ex.  153.  —  To  make  the  hydrate,  Mn  H2  02,  proceed  just 
as  in  Ex.  149  with  zinc,  using  MnSO4. 

What  is  the  color  of  this  manganous  hydrate? 
Is  it,  like  the  zinc  hydrate,  soluble  in  excess  ? 
What  change  happens  if  it  is  left  in  the  air  ? 

The  pure  manganous  hydrate  is  white,  but  it  is  changed 
by  oxygen  into  brown  manganic  hydrate. 

Ex.  154.  —  To  a  few  cubic  centimeters  of  the  manganous 
solution,  add  as  much  ammonium  chloride,  and  then  add 
ammonia  as  before. 


THE    IRON    GROUP  210 

Do  you  get  the  precipitate  ?  If  not,  it  shows  that  man- 
ganous  hydrate  is  soluble  in  ammonium  chloride.  You 
will  get  none  of  it,  if  enough  of  this  chloride  is  present. 

PREPARATION  OF  POTASSIUM  MANGANATE. —  The  man- 
ganate  is  soluble  in  water,  and  of  course  it  cannot  be  pre- 
cipitated. But  there  is  another  way  of  making  salts,  and 
that  is  by  fusion,  or,  as  it  is  often  called,  the  "dry  way." 

Let  us  mix  a  little  "  black  oxide "  of  manganese  with 
an  equal  weight  of  solid  potassium  hydroxide  and  half  as 
much  potassium  chlorate.  This  mixture  should  be  strongly 
heated.  It  may  be  done  in  a  thin  iron  spoon,  or  the  bottom 
of  a  broken  porcelain  dish.  When  well  fused,  the  mass  will 
turn  green,  and  this  green  substance  is  potassium  manga- 
nate,  K2Mn  04.  Let  it  cool  and  then  put  it  into  water,  and 
you  shall  find  that  the  manganate  dissolves,  yielding  a  fine 
green  solution. 

PREPARATION  OF  PERMANGANATE.  —  If  now  you  boil 
some  of  this  green  solution,  you  shall  see  its  color  change 
to  a  rich  purple-red.  The  fact  is,  that  the  green  manganate 
is  easily  oxidized,  and  is  thus  changed  into  the  red  perman- 
ganate, K2Mn208.  This  change  takes  place  on  boiling  its 
solution.  The  curious  change  of  color,  from  green  to  red, 
has  given  to  the  manganate  the  name  "chameleon  mineral.'' 
The  permanganate  holds  its  oxygen  very  loosely,  and  will 
therefore  oxidize  other  bodies  readily.  By  this  action  it 
decomposes  organic  matter.  When  added  to  water  contain- 
ing organic  matter,  it  becomes  colorless  or  brown  by  giving 
up  its  oxygen. 

Nickel.  Ni" Nickel  is  a  white,  hard  metal,  which  is 

much  like  iron,  but  does  not  rust  as  easily,  and  on  this 
account  it  is  used  as  a  plating  on  the  surface  of  other 
metals,  such  as  steel,  copper,  and  brass. 

Nickel  salts  are  generally  green,  but  the  description  of 
them  need  not  detain  us. 


220  THE    IRON    GROUP 

Cobalt.  Co" Cobalt  is  more  rare  than  nickel.  It 

also  is  a  hard,  white  metal,  with  a  reddish  tinge  however, 
and  in  other  qualities  it  is  much  like  nickel  and  iron.  The 
salts  of  cobalt  are  highly  colored,  and  the  color  depends 
on  whether  they  contain  water.  Thus  cobaltous  sulphate, 
when  it  contains  water,  CoS04,  7H20,  is  a  beautiful  red 
salt,  but  once  drive  its  water  off  by  heat,  and  the  sulphate, 
CoS04,  is  blue.  The  silicate  is  used  to  color  glass;  so  is 
the  oxide.  For  this  purpose  no  substance  yields  a  richer 
blue.  The  blue  glass  used  in  viewing  colored  flames  is  an 
example. 

The  student  should  prepare  some  nickel  and  cobalt  salts 
and  study  them  by  making,  with  them,  the  same  experi- 
ments as  have  been  already  made  with  salts  of  zinc  and 
manganese. 

IRON.    Fe"  or  (Fe2)vl. 

While  manganese,  nickel,  and  cobalt  are  quite  rare  and 
little  used,  iron  is  the  most  abundant  and  the  most  useful 
of  metals. 

Occurrence  in  Nature.  —  Iron  is  found  in  the  rocks, 
in  the  soil,  in  plants,  and  in  the  bodies  of  animals.  There 
is  no  metal  more  widely  diffused  than  iron. 

Native  iron  is  sometimes  found  in  the  earth,  and 
"meteoric  stones,"  which  come  from  space  outside  the 
earth,  are  little  else  than  iron,  with  also  some  native  nickel 
and  cobalt. 

The  sulphide,  FeS2,  "pyrites"  is  found  almost  every- 
where, sometimes  in  yellow  scales,  sometimes  in  perfect 
cubes,  which  are  also  yellow.  It  is  so  often  mistaken  by 
the  ignorant  for  a  precious  metal,  that  it  is  called  "  fool's 
gold." 

The  chief  ores  of  iron  are  two  oxides  and  a  carbonate. 
The  richest  of  all  is  the  "  Magnetic  oxide,"  Fe3O4,  which  is 
so  called  because  it  is  able  to  attract  a  magnet.  It  is  very 


THE   IRON    GROUP.  221 

abundant  in  this  country.  There  are  mountains  of  it  in 
Missouri,  and  vast  beds  of  richest  quality  in  New  York. 
It  is  black. 

Haematite  is  the  other  oxide,  Fe203.  It  is  red  or  brown, 
and  sometimes,  in  the  form  of  beautiful  crystals,  its  color 
is  dark  steel-gray. 

The  carbonate,  Fe  C  O3,  is  still  less  rich  in  iron,  and  it  is 
generally  mixed  with  clay  and  other  earthy  matters,  which 
make  it  poorer  still.  Such  a  carbonate  is  called  "clay-iron 
stone." 

These  ores  are  rarely  pure ;  they  are  largely  mixed  with 
sulphides  and  earthy  matter,  and  the  red  oxide  contains 
water;  it  is  Fe203,  3H20.  All  these  facts  have  to  be 
taken  into  the  account  in  the  process  of  extracting  the  iron. 

ROASTING  THE  ORES.  —  In  working  other  ores  than  the 
best  oxides,  they  are  first  roasted,  p.  213.  In  this  process 
water  is  driven  off,  sulphur  is  burned  into  sulphurous 
oxide,  carbon  dioxide  is  set  free  from  the  carbonate,  and 
the  iron  of  the  whole  is  changed  into  oxide,  which  re- 
mains mixed  with  the  earthy  matters  of  the  ore. 

REDUCING  THE  OXIDE.  —  The  next  thing  to  be  done  is 
to  decompose  the  oxide  and  liberate  the  iron.  The  power 
of  hot  carbon  to  reduce  an  oxide,  Ex.  72,  is  here  applied. 

The  process  is  carried  out  in  a  blast-furnace, — a  furnace 
in  which  the  fire  is  driven  by  a  blast  of  air.  Such  a  fur- 
nace is  pictured  in  Fig.  64.  It  may  be  50  or  100  feet  high, 
and  at  its  widest  place  inside  it  may  be  12  or  18  feet  in 
diameter.  The  furnace  is  fed  from  the  top,  and  kept  full 
of  fuel,  crushed  ore,  and  fragments  of  limestone,  thrown 
in  together. 

The  fire  is  started  at  the  bottom,  and  is  urged  to  the 
greatest  intensity  by  a  blast  of  air  driven  in  by  the  power 
of  a  steam-engine. 

In  this  intense  heat  the  earthy  parts  of  the  ore,  and  the 


222 


THE    IKOX    GROUP. 


limestone,  melt  together  into  a  glassy  substance,  called  the 
"slag."  The  carbon  of  the  fuel  seizes  the  oxygen  of  the 

ore  and  sets  the  iron 
free.  Kept  melted  by 
the  intense  heat,  the 
iron  runs  to  the  bottom 
of  the  furnace  into  a 
sort  of  chamber  made 
to  receive  it,  while  the 
lighter  slag  floats  on 
the  surface  of  the  melt- 
ed metal. 

In  front  of  the  fur- 
nace is  a  large  level  bed 
of  sand,  with  one  main 
fin-row  through  its  cen- 
ter, and  many  branch 
furrows  on  either  side, 
as  shown  in  the  cut. 

At  intervals  of  about 
twelve  hours  the  fur- 
nace is  opened  at  the 

bottom  for  the  metal  to  run  out.  It  then  flows  down  into 
the  furrows  of  the  sand-bed,  where  it  is  allowed  to  grow 
cold. 

The  iron  thus  made  is  called  cast-iron,  and,  in  the  form 
of  the  short  bars  made  in  the  sand,  it  is  called  pig-iron. 

But  besides  iron  this  cast-iron  contains  carbon,  silicon, 
sulphur,  and  phosphorus,  in  small  quantities.  These  im- 
purities make  the  metal  weak,  brittle,  and  fusible.  Never- 
theless, it  is  used  for  the  manufacture  of  a  great  many 
articles  where  great  strength  is  not  required. 

In  fact,  pure  iron  is  not  found  at  all  in  commerce.  The 
very  purest  contains  a  little  carbon. 


THE    IRON    GROUP. 


223 


The  Three  Forms  of  Iron.  —  There  are  three  forms 
of  iron,  known  as  cast-iron,  wrought-iron,  and  steel. 

WROUGHT-IRON.  —  This  is  the  purest  form  of  commercial 
iron ;  it  is  the  toughest,  strongest,  and  most  malleable.  It 
is  made  from  cast- 
iron  by  robbing 
it  of  its  impuri- 
ties, and  this  is 
done  by  bringing 
oxygen  into  con- 
tact with  all  parts 
of  the  melted 
metal.  The  fur- 
nace in  which 
this  is  done  is 
called  a  rever- 
berator?/ furnace, 
and  by  help  of 
the  cut,  Fig.  65,  the  operation  may  be  understood. 

The  cast-iron  is  placed  upon  a  large  hearth,  D ;  the  fire 
is  built  in  a  separate  part  of  the  chamber.  Flame  and  hot 
gases  from  the  fire  strike  against  the  arched  roof  of  the 
furnace,  and  the  intense  heat  is  thrown  from  the  roof  down 
upon  the  cast-iron.  In  a  little  time  the  iron  begins  to 
soften,  and  at  length  it  becomes  a  pasty  mass  of  half- 
melted  metal.  Then  the  furnace-man  unstops  a  hole,  />, 
thrusts  a  paddle  through  it  into  the  pasty  mass,  and  work- 
ing this  paddle  about  (puddling)  he  thoroughly  stirs  the 
metal,  so  that  all  parts  of  it  are  slowly  brought  in  contact 
with  the  hot  air  at  the  surface. 

The  hot  oxygen  of  the  air  seizes  the  impurities,  one 
after  another.  Some  of  the  new  compounds  form  a 
liquid  slag,  which  is  drawn  off  out  of  the  furnace  at  b, 
while  others  are  gases  which  pass  up  and  out  of  the  high 
chimney. 


Fig.  65. 


224  THE    IROX    GROUP. 

The  result  is,  that  the  iron  is  soon  left  almost  free  from 
its  impurities.  A  large  part  of  its  carbon  has  been  burned 
away,  and  has  gone  off  as  carbon  dioxide.  A  large  part 
of  the  other  impurities  are  also  burned,  but  some  of  the 
slag,  thus  made,  is  still  mixed  with  the  purified  iron. 

The  furnace-man  then  lifts  out  a  ball  of  this  pasty  iron, 
weighing  perhaps  sixty  pounds,  or  even  more,  and  puts  it 
under  the  heavy  blows  of  an  immense  hammer,  or  some- 
times under  the  tremendous  pressure  of  the  squeezer.  In 
this  way  the  impurities  which  are  still  mixed  with  the 
iron  are  pounded  or  squeezed  out,  so  that  the  iron  is  left 
more  pure  and  compact. 

The  mass  of  iron  is  then  forced  through  grooves  between 
two  strong  rollers.  The  very  great  pressure  of  these 
rollers  lengthens  the  mass  out  into  a  slender  rod  or  bar. 

For  the  best  quality  of  bar-iron,  as  this  form  is  often 
called,  the  bars,  made  by  the  first  rolling,  are  cut  into 
short  lengths  and  bound  together  in  bundles,  to  be  heated 
over  again  and  rolled  into  bars  a  second  time.  By  re- 
peating these  efforts  the  purest  and  strongest  iron  to 
be  found  in  commerce  is  obtained.  It  is  u'rouyht-iron, 
also  called  malleable  iron. 

STEKL.  —  Neither  cast-iron  nor  wrouyht-iron  has  the 
qualities  which  render  iron  useful  in  all  the  various  ways 
in  which  this  metal  is  employed ;  a  third  form,  which  is 
better  than  either  of  these  for  many  uses,  is  steel. 

The  difference  between  steel  and  the  other  two  kinds  of 
iron  is  best  shown  by  the  action  of  fire  and  water. 

Let  wrought-iron  be  strongly  heated  and  then  suddenly 
cooled  by  a  plunge  into  cold  water.  Very  little  if  any 
change  will  be  produced. 

Let  steel  be  treated  in  the  same  way,  and  it  will  be  made 
almost  as  hard  as  diamond,  and  so  brittle  that  it  will  snap 
before  it  will  bend.  Let  this  brittle  steel  be  heated  again 


THE    IRON    GROUP.  225 

to  a  point  below  red-heat  and  then  cooled,  and  it  is  softened 
somewhat,  and,  what  is  more  remarkable,  it  is  made  so 
elastic  that  it  will  bend  rather  than  break,  and  spring 
back  again  when  released  from  the  force. 

Cast-iron  may  be  hardened  as  much  as  steel  may  be,  but 
it  cannot  be  made  elastic. 

With  this  difference  in  properties  we  find  a  difference 
in  composition,  for  while  each  is  composed  of  iron  and 
carbon,  it  is  found  that  cast-iron  contains  the  largest  pro- 
portion of  carbon,  wrought-iron  the  smallest,  and  steel  a 
proportion  between  the  other  two. 

It  would  seem,  then,  that  steel  could  be  made  in  two 
ways : 

By  taking  away  some  carbon  from  cast-iron. 

By  adding  some  carbon  to  wrought-iron.  And,  in  fact, 
the  steel  so  largely  used  in  the  arts,  is  made  in  both  these 
ways.  Thus : 

1.  From  two  to  six  tons  of  cast-iron  is  melted  and 
then  run  into  a  large  globe-shaped  vessel  made  of  a  sub- 
stance which  will  not  melt  at  the  highest  heat  to  be 
attained.  In  the  bottom  of  this  vessel  there  are  many 
holes,  and  a  strong  blast  of  air  is  driven  through  them. 
The  air  bubbles  up  through  the  melted  metal,  and  a  most 
furious  burning  begins.  The  oxygen  attacks  the  silicon, 
and  the  sulphur,  and  the  carbon,  and  some  of  the  iron  also, 
and  burns  them  into  compounds  with  itself. 

In  this  way  the  iron  is  partly  purified,  but  the  chemical 
action  goes  too  far,  and  removes  so  much  carbon  that  too 
little  is  left.  By  adding  some  cast-iron  to  the  purified 
mass,  enough  carbon  is  given  back  to  change  the  whole  into 
steel. 

The  globe-shaped  vessel  (converter)  is  then  turned  on  its 
pivots,  and  the  melted  steel  is  run  out  into  a  ladle,  and 
then  poured  into  moulds. 


226  THE  inox  uvour. 

Less  than  half  an  hour  is  time  enough  to  change  these 
tons  of  cast-iron  into  steel.  The  process  is  called  the 
Bessemer  process. 

2.  In  the  other  way  of  making  steel,  bars  of  wrought- 
iron  are  packed  in  charcoal,  and  the  two  are  shut  up  to- 
gether in  air-tight  boxes.  They  are  then  made  red-hot,  and 
are  kept  so  for  several  days. 

During  this  heating,  carbon  finds  its  way  into  the  solid 
iron  and  changes  the  whole  mass  to  steel.  This  product 
is  known  as  blistered  steel,  because  the  bars,  on  coming  out 
of  their  hot  bed,  are  found  to  have  a  great  many  bubbles 
or  blisters  on  their  surface.  The  steel  is  then  melted  and 
run  into  moulds.  This  method  of  making  steel  is  called 
cementation. 

Compounds  of  Iron.  _  Some  facts  about  the  chemical 
action  of  iron  have  been  noticed  already.  The  production 
of  ferrous  sulphate  in  Ex.  120,  and  of  ferrous  chloride  in 
Ex.  94,  showed  the  action  of  iron  on  acids,  —  the  most  direct 
way  of  making  some  salts  of  this  metal. 

Experiments  96  and  97  are  still  more  instructive.  They 
should  now  be  studied  over  again,  because  they  prove  that 
there  are  two  distinct  chlorides  of  iron,  —  the  ferrous  chlo- 
ride, FeCl.,,  and  the  ferric  chloride,  Fe2Cla.  And  this 
illustrates  a  most  important  fact,  for  iron  forms  not  only 
two  chlorides,  but  also  two  sulphates,  two  nitrates,  and, 
in  fact,  two  large  classes  of  salts,  —  the  ferrot/«  salts,  such 
as  ferrous  chloride,  and  the  ferric  salts,  such  as  ferric 
chloride. 

COMPARE  THE  FERROUS  AND  FERRIC  COMPOUNDS.  —  These 
two  classes  of  iron  compounds  are  unlike  in  appearance, 
and  quite  different  in  their  chemical  behavior.  These 
differences  are  most  distinctly  shown  by  experiments.  In 
the  first  place 

Ex.  155.  —  Make  some  ferrous  and  some  ferric  chloride, 


THE    IRON    GROUP  227 

to  be  used  in  the  work  which  follows.  To  do  this  use  clip- 
pings of  small  iron  wire,  or  small  nails,  and  add  them  to 
hydrochloric  acid  and  aqua  regia  until  these  liquids  will  dis- 
solve no  more.  For  directions,  see  Ex.  96  and  Ex.  97.  The 
hydrochloric  acid  yields  solution  of  ferrous  chloride.  The 
aqua  regia  yields  solution  of  ferric  chloride. 

Note  the  colors  of  these  solutions. 

Ferrous  salts  are  generally  light  green ;  while  ferric 
salts  are  generally  reddish  yellow  or  brown. 

Ex.  156.  —  Prepare  two  test-tubes,  each  with  about  10  cc. 
of  water,  and  add  to  one,  1  cc.  of  the  ferrous  chloride  and 
to  the  other,  1  cc.  of  the  ferric  chloride.  Now  add  ammo- 
nium hydroxide  in  drops  to  the  first,  and  notice  the  precipi- 
tate which  forms.  Afterward  treat  the  second  in  the  same 
way.  The  ferrous  chloride  yields  ferrous  hydroxide, 
Fe(HO)2.  The  ferric  chloride  yields  ferric  hydroxide, 
Fe2(HO)(j.  The  color  of  the  first  is  light  green,  of  the 
second  brownish  red. 

Now  filter  the  ferrous  precipitate  out,  and  leave  it  on  the 
paper  in  the  air.  You  will  find  it  turning  red  like  the 
other  hydroxide.  In  fact,  the  moist  ferrous  hydroxide 
actually  changes  into  the  ferric  hydroxide.  Thus: 

2  Fe  (H  0)2  +  H2  O  +  O  =  Fe2  (II  O)6 . 

So  it  is  also  with  other  iron  compounds  of  the  ous  class  : 
the  air  oxidizes  them  into  the  ic  form.  This  illustrates 
the  rusting  of  iron  in  moist  air:  this  same  reddish  hy- 
droxide is  made.  We  then  call  it  iron-rust. 

But  the  ous  compounds  become  ic  compounds  by  the 
action  of  other  oxidizing  agents  than  air,  —  such  as  nitric 
acid.  Thus : 

Ex.  157.  —  Put  about  1  cc.  of  ferrous  chloride  with  about 
5  cc.  of  water  in  a  tube,  add  4  or  5  drops  of  strong  H  N  03, 
and  then  boil  it  gently  for  a  minute. 


228  THE    IKON    GROUT. 

Notice  a  change  in  the  color  of  the  solution. 

What  change  in  the  substance  does  this  color  suggest  ? 

Now  add  ammonium  hydroxide,  and  observe  the  precipi- 
tate. Is  it  green  or  red,  — ferrous  or  ferric  hydroxide  ? 

What  change  does   this   prove   that   the  H  N  03  made  ? 

The  nitric  acid  will,  in  the  same  way,  change  other  ous 
iron  compounds  into  the  ic  form.  It  is  said  to  oxidize  them, 
and  yet  it  does  not  change  them  into  oxides.  It  changed 
the  Fe  C12  into  the  Fe2  C10,  and  it  would  change  Fe  S  O4  into 
Fe.,  (S  04)3.  Whatever  changes  any  compound  from  a  lower 
to  a  higher  form  of  combination  is  called  an  oxidizing  a  gent. 

Ex.  158.  —  Put  two  or  three  drops  of  ferrous  chloride 
with  about  5  cc.  of  water,  and  then  add  drops  of  a  solution 
of  potassium  ferrocyanide. 

In  another  tube  make  the  same  experiment  with  ferric 
chloride.  Note  the  different  results  carefully. 

A  beautiful  deep  blue  precipitate  is  always  made  by 
potassium  ferrocyanide  in  ferric  salts:  it  is  "Prussian 
blue."  The  same  reagent  in  ferrous  salts  yields  a  pale  blue 
precipitate,  and  this  difference  is  so  marked,  that  one  can, 
in  this  way,  tell  whether  a  given  iron  solution  holds  a 
ferrous  or  a  ferric  salt. 

COMPARE  SOME  COMPOUNDS  OF  IRON  WITH  THOSE  OF 
ZINC  AND  MANGANESE.  Ex.  159.  —  Put  a  few  drops  of 
ferric  chloride  in  water,  and  add  ammonium  hydroxide  "  in 
excess,"  to  see  whether  ferric  hydroxide  is  soluble  in 
excess,  like  that  of  zinc,  Ex.  149. 

Ex.  160.  —  Put  a  few  drops  of  ferric  chloride  into  a  little 
water,  add  considerable  ammonium  chloride,  and  then  the 
ammonium  hydroxide,  to  see  whether  the  ferric  hydroxide 
is  soluble  in  Am  Cl,  like  that  of  manganese,  Ex.  154. 

Ex.  161.  —  To  10  cc.  of  water  with  1  cc.  of  ferric  chloride 
add  a  few  drops  of  ammonium  sulphide,  Am2S. 


THE   IRON    GROUP.  229 

What  is  the  name  and  the  color  of  this  precipitate  ? 
Compare  it  with  the  sulphides  of  zinc  and  manganese. 

Ex.  162.  —  To  1  cc.  of  ferric  chloride  add  a  drop  or  two 
of  hydrochloric  acid,  and  then  add  a  solution  of  hydrogen 
sulphide.  Does  the  color  of  this  result  agree  with  that  of 
any  of  the  iron  compounds  seen  before  ? 

Ferrous  sulphide,  Fe  S,  is  a  black  substance  which  is 
not  soluble  in  alkaline  liquids,  but  is  soluble  in  acids.  For 
this  reason  it  is  made  by  Am2S,  but  not  by  H2S.  In  this 
respect  it  is  like  the  sulphides  of  zinc  and  manganese.  The 
whiteness  of  the  liquid  in  Ex.  162  is  due  to  sulphur.  The 
H2S  is  decomposed  by  the  ferric  chloride,  and  its  sulphur 
is  set  free. 

Chromium.  Cr.  —  Chromium  maybe  made  by  heating 
its  chloride  with  potassium,  it  is  then  a  dark  gray  powder, 
which  in  air  takes  fire  before  it  reaches  a  red  heat.  But  if 
the  chloride  is  heated  with  sodium,  instead  of  potassium, 
the  chromium  is  set  free  as  hard  and  shining  crystals. 
While,  if  the  metal  is  made  from  its  oxide,  by  heating 
it  with  charcoal,  it  has  a  steel-gray  luster,  is  hard  enough 
to  cut  glass,  and  combines  with  oxygen  slowly  when  heated 
in  the  air.  It  is  a  curious  fact  that,  if  we  make  the  same 
substance  in  different  ways,  it  sometimes  comes  out  with 
different  properties,  as  in  this  case  of  chromium. 

In  its  chemical  actions,  chromium  is  sometimes  a  metal 
and  sometimes  not.  With  acids  it  forms  salts,  like  other 
metals,  such  as  chromium  sulphate,  Cr^SO^.  But  with 
bases  it  forms  salts,  like  the  non-metals,  such  as  potassium 
chromate,  K2Cr()4.  Is  it  nature,  or  only  the  chemist, 
who  divides  the  elements  into  metals  and  non-metals  ? 

The  chief  ore  of  this  metal  is  chromite,  a  compound  of 
iron  chromium  and  oxygen.  It  is  not  the  metal  itself 
which  is  obtained  from  this  chromic  iron,  but  its  more  use- 
ful compounds. 


230  THE    IRON    GROUT. 

Let  the  chromite  be  heated  with  a  mixture  of  potassium 
carbonate  and  potassium  nitrate,  and  the  potassium  will 
take  the  place  of  the  iron.  In  this  way  the  ore,  iron  chro- 
mite, is  changed  into  potassium  chromate,  KaCr04.  This 
new  chromate  can  then  be  washed  out  with  water.  The 
solution  is  very  yellow,  and  when  evaporated  yields  a 
highly-colored  yellow  salt. 

Now  let  a  solution  of  this  K2  Cr  04  be  treated  with  nitric 
acid.  Its  color  will  change  from  yellow  to  red  (try  it),  and 
its  substance  will  change  from  potassium  chromate  to 
potassium  dichromate,  K2Cr<jO7.  By  evaporating  the 
solution,  fine  orange-red  crystals  may  be  obtained.  (Do 
this.) 

Compounds  of  Chromium.  — The  chromates  generally 
are  highly  colored,  and  some  of  the  insoluble  ones  are 
used  as  paints.  The  lead  chromate,  or  "chrome-yellow"' 
as  it  is  known  in  commerce,  is  a  good  example. 

Ex.  163.  —  Make  a  solution  of  either  potassium  dichro- 
mate or  chromate,  in  water,  and  add  little  by  little  some 
solution  of  lead  acetate.  The  bright  yellow  precipitate  is 
the  pigment,  chrome-yellow,  PbCrO4. 

Salts,  such  as  chromium  sulphate,  in  which  the  chro- 
mium is  basic,  are  sometimes  violet-colored,  sometimes 
green. 

Chrome  alum  is  a  quite  common  substance  made  of  two 
sulphates,  the  chromium  and  potassium  sulphates.  It  has 
a  fine  violet  color.  From  this  compound  we  can  easily 
get  chromium  hydroxide,  which  is  green.  Thus : 

Kx.  164-  —  To  a  solution  of  a  little  chrome  alum  in 
water,  add,  little  by  little,  some  ammonium  hydroxide. 
Notice  the  bluish-green  precipitate  of  Cr2  (H  0)6. 

Is  this,  like  the  zinc  hydroxide,   soluble  in  excess? 
Is  it,  like  the  manganese  hydroxide,  soluble  in  Am  Cl  ? 


THE   IRON    GROUP.  231 

Will  it,  like  the  ferrous  hydroxide,  turn  red  when  ex- 
posed to  air  ? 

Can  you  get  the  same  precipitate  by  K  H  0  instead  of 
NH4HO? 

And  if  so,  is  it  soluble  in  excess  of  K  H  0  ? 

Ex.  165.  —  To  a  solution  of  a  little  chrome  alum  in 
water  add  Am2  S,  little  by  little,  and  compare  this  pre- 
cipitate with  that  in  the  last  experiment.  It  is  the  same 
substance. 

There  is  a  chromium  sulphide,  Cr2S3,  but  it  cannot  be 
made  in  the  presence  of  water,  like  the  sulphides  of  man- 
ganese, zinc,  and  iron ;  the  hydroxide  will  come  instead. 

THE  IRON   GROUP. 

The  five  metals  —  iron,  manganese,  nickel,  cobalt,  and 
chromium  —  are  closely  related,  and,  together,  form  the 
Iron  Group. 

The  metals  in  this  group  are  much  alike  in  color,  luster, 
and  hardness,  and  much  alike  in  chemical  behavior.  For 
example,  they  all  unite  with  oxygen,  and  in  more  propor- 
tions than  one,  making  oxides  which  are  sometimes  basic 
and  sometimes  acid. 

But  their  affinity  for  oxygen  is  not  equally  strong,  for 
while  chromium  and  manganese  rust  quickly  when  exposed 
to  moist  air,  iron  does  so  much  more  slowly,  while  nickel 
and  cobalt  will  keep  their  luster  unless  heated.  It  is  in- 
teresting to  note  that  this  order  of  the  metals,  in  their 
behavior  with  oxygen,  is  also  the  order  of  their  combin- 
ing weights.  Thus : 

Cr        Mn        Fe        Ni        Co 

52          55          56         58         59 

Another  fact  is  curious :  these  atomic  weights  are  nearly 
alike.  In  other  groups  we  have  not  found  it  so.  Look,  for 
example,  at  the  potassium  and  the  calcium  groups. 


232  THE    IRON    GROUP. 

SUGGESTIONS.  —  If  the  student  has  made  the  experiment  with 
the  ammonium  sulphide,  Am2  S,  he  has  seen  how  very  different 
are  the  sulphides  of  zinc,  manganese,  iron,  and  chromium.  And 
if  he  has  used  ammonium  hydroxide,  N  H4  H  O,  he  has  also  seen 
how  very  different  are  the  hydroxides  of  these  metals.  Now,  by 
the  experiment  with  these  two  reagents,  he  ought  to  be  able  to 
tell  with  considerable  certainty  whether  any  substance  which  is 
given  him  is  a  compound  of  one  or  another  of  these  metals. 

Let  him  try  to  do  this  by  "taking  specimens  from  the  teacher  or 
a  friend  who  knows  what  they  are.  Nickel  and  cobalt  may  also 
be  included  in  the  list,  if  thought  best. 

If  the  substance  given  will  not  dissolve  in  water,  perhaps  you 
can  change  it  into  another  compound,  of  the  same  metal,  which 
will.  Ferrous  sulphide  is  not  soluble  in  water,  but  hydrochloric 
acid  will  change  it  into  ferrous  chloride,  which  is.  Now,  sup- 
pose you  do  not  know  that  the  specimen  is  ferrous  sulphide,  and 
yet  you  wish  to  find  out  if  it  is  a  compound  of  iron  or  of  some 
other  metal.  You  can  treat  it  with  a  little  hydrochloric  acid  and 
get  a  solution  of  the  chloride,  and  then  you  can  use  the  Am2  S 
and  the  N  H4  H  O. 

If  hydrochloric  acid  will  not  answer,  you  can  use  nitric  acid, 
or  even  aqua  regia,  to  get  the  substance  into  solution.  But  in 
all  cases,  just  as  little  of  these  acids  as  possible  should  be  used. 


AIitJMINXftf.    Al". 

ALUMINUM  is  a  beautiful  blue  metal,  with  a  luster  like 
silver.  It  can  be  hammered  into  thin  sheets,  or  dra.wn 
into  fine  wire,  or  cast  into  any  desired  form,  like  iron.  It 
is  one  of  the  light  metals ;  it  is  only  2.56  times  heavier 
than  water.  It  does  not  easily  tarnish  in  air,  and  it  melts 
only  at  a  high  temperature. 

At  the  same  time  that  it  has  all  these  valuable  proper- 
ties, aluminum  is  one  of  the  most  abundant  metals.  It 
is  found  combined  with  silica  in  clay,  and  in  all  slate 
rocks,  which  are  little  more  than  hardened  clay.  In  fact, 
about  one-twelfth  the  weight  of  the  solid  parts  of  the 
earth  is  aluminum. 

But  there  is  no  cheap  way  to  get  this  metal  from  its 
ores,  and  it  is,  therefore,  too  costly  to  be  used  in  the  arts, 
in  place  of  silver  and  iron,  for  many  purposes,  as  it  would 
otherwise  be.  Its  use  is  limited  to  ornamental  work,  and 
to  small  articles  of  apparatus  where  strength  with  light 
ness  are  required. 

'  Compounds  of  Aluminum.  —  Alum  is  the  most  useful 
compound  of  this  metal.  Alum  is  really  a  compound  of 
two  sulphates  and  water,  for  it  is  potassium  and  alumi- 
num sulphate  with  much  "  water  of  crystallization."  Its 
formula  is  K2A12(SO4)4  +  24H20.  This  is  the  common 
alum,  although  "  ammonium  alum "  is  also  much  used  in- 
stead; it  has  ammonium  in  place  of  potassium. 

Aluminum  oxide,  or  alumina  as  it  is  usually  called,  is 
found  in  the  rocks  in  beautiful  crystals,  having  different 
colors  and  known  by  different  names.  The  topaz  and  the 
emerald  are  examples ;  the  first  is  yellow  and  the  second 
green,  but  both  are  alumina.  So  are  the  oriental  amethyst, 


234 


which  is  purple,  the  sapphire,  which  is  blue,  and  the  ruby, 
which  is  red. 

Some  compounds  of  aluminum  are  largely  used  in  oper- 
ations of  calico  printing  and  dyeing.  This  is  true  of  the 
sulphate  and  the  hydroxide. 

The  following  experiments  will  reveal  some  of  the  chemi- 
cal characters  of  the  aluminum  compounds. 

Ex.  166.  —  Make  a  dilute  solution  of  alum,  and  add,  little 
by  little,  NH4H  O.  The  white  gelatine-like  precipitate  is 
aluminum  hydroxide,  A12(HO)6. 

Is  this  A12(HO)6  soluble  in  excess? 

Can  you  get  it  by  means  of  K  H  O  instead  of  N  H4  H  0  ? 

And  if  so,  is  it  soluble  in  excess  of  K  H  0  ? 

Ex.  167.  —  Make  a  dilute  solution  of  alum  as  before,  and 
color  it  just  distinctly  red  with  a  solution  of  cochineal. 
Then  add  N  H4  H  O.  The  aluminum  hydroxide  now  com- 
bines with  the  coloring-matter  of  the  cochineal.  It  is  red, 
while  the  liquid  is  left  colorless. 

The  color  cannot  be  washed  out  of  the  hydroxide.  Now, 
it  is  this  fact  which  makes  the  aluminum  salt  useful  in 
dyeing.  For  if  cloth  is  first  soaked  in  a  solution  of  alum 
and  coloring-matter,  and  then  plunged  into  a  solution  of 
ammonia,  the  same  reaction  will  take  place  in  the  filers 
of  the  fabric,  from  which  the  color  cannot  afterward  be 
washed  out  by  water. 

Ex.  168.  —  To  a  dilute  solution  of  alum  add  a  few  drops 
of  Am2S,  and  compare  the  precipitate  with  that  in  Ex.  167. 
It  is  the  same  substance. 

There  is  a  sulphide  of  aluminum,  A12SS,  but  water 
decomposes  it  at  once,  changing  it  to  the  hydroxide.  On 
this  account  the  sulphide  cannot  be  made  in  solutions.  In 
this  respect  aluminum  is  like  chromium. 


THE    ANTIMONY    GROUP. 

Antimony.  Sb"' Tins  metal  is  now  and  then  found 

native,  but  it  is  oftener  found  in  combination  with  sulphur 
or  oxygen.  The  chief  ore  is  the  antimony  sulphide,  Sb2S3. 

The  metal  has  a  silvery  appearance,  quite  brilliant, 
but,  unlike  silver,  it  is  very  brittle.  Its  alloys  are  more 
important  than  itself.  We  only  need  to  mention  type- 
metal,  which  is  far  the  most  important  of  all  alloys,  since 
the  art  of  printing  depends  upon  it.  Antimony,  tin,  and 
lead  are  melted  together  to  make  this  alloy,  from  which 
all  types  for  printing  are  cast. 

There  are  three  oxides  of  antimony,  and  these  are  all 
inclined  to  form  acids  rather  than  bases.  This  shows  that 
antimony  is  more  like  the  non-metals  than  any  other  metal 
which  has  yet  been  described.  Another  evidence  of  this  is 
the  fact  that  antimony  combines  with  hydrogen,  just  as  do 
nitrogen  and  phosphorus.  The  compound  is  called  stibine, 
and  its  formula  is  H3  Sb.  Stibine  may  be  made  and  burned 
just  like  arsine,  Ex.  123,  and  it  then  yields  a  stain  of  anti- 
mony on  porcelain  by  Marsh's  test,  p.  181. 

Bismuth.  Bi'".  —  This  metal  is  crystalline,  brittle,  and 
bright,  with  a  reddish  color.  Bismuth,  like  antimony,  forms 
an  alloy  with  lead  and  tin.  This  alloy  is  called  fusible 
metal,  and  it  merits  this  title  because  it  melts  at  a  tem- 
perature of  only  94°  C.  The  separate  metals  must  be 
heated  much  higher:  tin  melts  at  228°,  bismuth  at  267°, 
and  lead  at  325°,  but  this  alloy  at  94°.  Such  is  very 
generally  the  case  with  alloys :  they  melt  more  easily 
than  any  one  of  the  metals  of  which  they  are  made. 

235 


236  THE   ANTIMONY    (1ROUP. 

Fusible  metal,  like  type-metal,  expands  when  it  becomes 
solid,  and  on  this  account  it  is  used  for  taking  casts 
from  medals.  When  cast  in  a  mold  it  expands  into  every 
line,  and  makes  a  most  beautiful  and  faithful  copy. 

Bismuth,  like  a  true  metal,  forms  bases,  and,  like  a  non- 
metal  also,  it  forms  acids.  But  its  metallic  nature  is  much 
more  distinct  than  that  of  antimony,  since  it  is  less  likely 
to  form  acids.  This  is  also  shown  by  the  fact  that  it  has 
no  compound  with  hydrogen. 

The  Group.  —  Bismuth  and  antimony  are  much  alike, 
and,  as  we  have  just  seen,  both  have  the  properties  of 
non-metals.  In  fact,  they  agree  closely  with  the  nitrogen 
group.  In  bismuth  the  metalMc  properties  are  very  clear, 
in  antimony  not  so  clear,  in  arsenic  quite  obscure,  in  phos- 
phorus and  nitrogen  altogether  wanting.  From  bismuth  to 
nitrogen,  the  transition  from  metal  to  non-metal  is  gradual 
and  perfect. 

No  better  proof  is  needed  that  it  is  the  chemist,  and 
not  nature,  who  divides  the  elements  into  these  two  great 
classes. 

Such  a  division,  however,  is  convenient.  But  chemists 
do  not  all  agree  as  to  just  where  the  line  shall  be  drawn. 
Some  have  put  arsenic  among  the  metals ;  others  have  put 
arsenic,  and  antimony  too,  among  the  non-metals. 

In  this  book  the  line  has  been  drawn  between  arsenic 
and  antimony.  Because,  then,  we  have  on  one  side,  all  the 
elements  whose  compounds  with  oxygen  and  hydrogen  are 
acids,  and  on  the  other,  all  those  whose  compounds  with 
oxygen  and  hydrogen  are  ever  bases.  The  oxides  of  arsenic 
are  always  acid,  while  one  of  the  oxides  of  antimony  is 
basic,  —  feebly  so  to  be  sure,  but  truly  basic. 

COMPARE  THEIR  REACTIONS.  —  Some  of  the  chemical 
actions  of  bismuth,  antimony,  and  arsenic  will  be  a  useful 
study  by  experiment. 


THE    ANTIMONY    GROUP.  237 

Ex.  169. — Arrange  three  tubes  each  with  about  10  cc, 
of  water.  Into  one  put  a  few  grains  of  arsenous  oxide ; 
shake  it  well,  and  if  it  does  not  dissolve,  heat  it.  It 
dissolves  to  a  clear  solution. 

Into  a  second  tube  put  a  few  grains  of  bismuth  nitrate ; 
shake  it  well :  you  find  the  liquid  changed  to  a  milky 
whiteness,  instead  of  a  clear  solution.  To  this  then  add 
strong  hydrochloric  acid,  drop  by  drop,  and  it  will  soon 
become  perfectly  clear. 

Into  the  third  tube  put  a  few  drops  of  antimony  chlo- 
ride ;  this  liquid  also  at  once  becomes  white.  But  add 
hydrochloric  acid  as  before,  and  it  becomes  clear. 

The  compounds  of  bismuth  and  antimony  are  decom- 
posed by  water,  but  of  arsenic  not.  This  effect  of  water  is 
not  common.  The  white  solids,  precipitated  by  water,  are 
soluble  in  hydrochloric  acid. 

These  three  clear  solutions  may  be  used  in  the  follow- 
ing experiments.  We  will  first  study  the  sulphides,  as 
follows : 

Ex.  170.  —  Fit  up  the  apparatus  for  hydrogen  sulphide, 
Ex.  107.  Put  an  arsenic  solution  —  enough  to  cover  the 
end  of  the  glass  tube  —  into  flask  a,  and  add  a  few  drops 
of  HC1.  Put  an  antimony  solution,  made  clear  by  H  CJ, 
into  flask  b,  and  a  bismuth  solution,  also  made  clear  by 
H  Cl,  into  flask  c,  and  then  pass  the  H2  S  gas  through 
them  all. 

Observe  that  the  sulphides  of  all  three  metals  are 
produced,  and  notice  their  different  colors. 

These  are  the  first  sulphides  which  we  have  found  to  be 
insoluble  in  acid  water.  And  of  these,  one,  the  orange-red 
antimony  sulphide,  is  soluble  if  much  H  Cl  is  present. 

Ex.  171.  —  Let  the  sulphides  settle,  and  then  pour  off 
the  liquid ;  add  considerable  water  to  each.  Let  the 


238  THE    ANTIMONY    GROUP. 

sulphides  settle,  and  decant  the  liquid  again.  We  repeat 
this  work  in  order  to  wash  the  sulphides  clean  :  do  it  once 
more.  Now  pour  yellow  ammonium  sulphide,  (X  H4  )2  S, 
upon  each,  and  gently  warm  it.  The  question  is,  whether 
the  sulphides  are  soluble  in  this  liquid.  The  bismuth 
sulphide  will  remain  unchanged,  but  the  other  two  should 
disappear ;  they  are  soluble  in  yellow  ammonium  sulphide. 

Ex.  172.  —  Next  compare  the"  hydroxides.  For  this  pur- 
pose make  three  clear  solutions,  as  in  Ex.  169,  only  be 
more  careful  to  not  use  more  HC1  than  just  enough  to 
dissolve  the  white  precipitates.  Then  add  N  H4  H  O,  little 
by  little,  to  each.  Observe  the  difference  between  the 
arsenic  and  the  other  two  solutions. 

QUERIES.  —  By  what  experiments  could  you  decide  whether  a 
given  substance  is  a  compound  of  aluminum  or  of  chromium? 

By  what  experiments  could  you  decide  whether  a  given  sub- 
stance is  a  compound  of  aluminum  or  of  iron? 

If  a^ given  substance  is  a  compound  of  aluminum,  or  else  of  a 
metal  in  the  antimony  group,  by  what  experiment  could  you 
decide  which  it  is? 

SUGGESTIONS.  —  Take  one  or  more  specimens  from  the  teacher 
or  a  friend  who  knows  what  they  are,  and  decide,  by  experiments, 
whether  each  is,  or  is  not,  a  compound  of  aluminum. 

Take  specimens,  which  may  be  compounds  of  any  one  of  the 
metals  in  the  antimony  group,  and,  by  experiments,  decide  which. 


TIN    AXD    I/EAD. 

Tin.  Sn".  —  Tin  seems  to  have  been  known  since  the 
earliest  periods  of  history. 

It  was  called  Jupiter  by  the  old  alchemists,  and  stan1  by 
the  people  of  Phoenicia.  The  people,  just  named,  dis- 
covered tin  in  Britain  more  than  a  thousand  years  before 
the  Christain  era. 

Tin  is  found  in  the  form  of  tinstone.  Tinstone  is  a 
compound  of  tin  and  oxygen,  Sn  02  ;  it  is  the  chief  ore 
of  the  metal. 

The  ore  of  tin  is  found  in  Cornwall,  England,  which 
has  been  noted  for  its  tin-mines  for  many  hundred  years. 
Bohemia,  Saxony,  and  Malacca  and  Banca,  in  India,  also 
yield  the  ore  of  this  metal.  In  this  country  it  seems  to 
be  very  rare,  but  it  has  been  found  in  New  Hampshire  and 
California. 

EXTRACTION  OP  THE  METAL.  —  To  obtain  tin  from  this 
ore  would  be  a  simple  thing  if  the  ore  were  pure ;  for  it 
is  an  oxide  which  can  be  reduced  by  carbon.  But  the  ore 
is  mixed  with  other  matters,  which  make  the  process  more 
difficult. 

To  get  rid  of  the  rocky  and  earthy  parts,  the  ore  is 
stamped  to  powder  under  wooden  stampers  shod  with  iron, 
and  then  washed  with  water.  To  get  rid  of  sulphur  and 
arsenic,  the  ore  is  roasted  and  washed,  perhaps  twice.  And 
then,  to  take  away  the  oxygen,  the  roasted  ore  is  melted 
with  charcoal  and  lime. 

PROPERTIES  OF  THE  METAL.  —  Tin  is  a  silver-white 
metal  with  a  fine  luster,  and  somewhat  harder  than  lead. 
It  can  be  hammered  into  sheets  so  thin  that  a  thousand 

1  The  symbol  for  tin,  Sn,  comes  from  its  old  name  Stan,  or  Stannum. 


240  TIN   AND    LEAD. 

or  more  would  be  needed  to  make  an  inch  in  thickness. 
It  does  not  tarnish  readily  in  air,  showing  that  its  attrac- 
tion for  oxygen  is  slight,  but  when  heated,  tin  and  oxygen 
combine  at  once. 

Because  tin  is  so  malleable  it  is  much  used  in  thin 
sheets,  called  tin-foil.  But  the  tin-foil  of  commerce  usually 
contains  some  lead,  and  sometimes  a  large  proportion  of 
that  metal. 

Because  air  does  not  readily  tarnish  it,  tin  is  used  for 
coating  iron  to  keep  it  from  rusting.  The  u  tin  "  of  which 
common  tin-ware  is  made  is  sheet-iron  with  a  thin  coat- 
ing of  tin. 

Compounds  of  Tin.  —  There  are  two  compounds  of 
oxygen  and  tin ;  one  is  called  stannous  oxide,  Sn"  O,  the 
other  is  the  stannic  oxide,  Sn""02.  There  are  also  two 
chlorides,  two  sulphates,  —  in  fact,  there  are  two  classes 
of  tin  compounds,  the  ous  and  the  ic  forms. 

Starting  with  the  metal  itself  we  can  make  several  of 
the  tin  compounds  and  study  by  experiment  their  chemi- 
cal behavior.  We  will  first  study  the  chlorides. 

Ex.  173.  —  Place  5  cc.  strong  hydrochloric  acid  in  a  test- 
tube  and  drop  into  it  a  piece  of  granulated  tin.  Then  heat 
until  the  effervescence  is  brisk ;  after  which  keep  the  tube 
warm  by  holding  it  above  the  flame  of  the  lamp  until, 
when  taken  away  from  the  heat,  the  bubbling  nearly  or 
quite  stops.  If,  before  this  occurs,  the  tin  is  used  up, 
another  piece  must  be  added.  When  the  effervescence  is 
brisk,  a  match-flame,  brought  to  the  mouth  of  the  tube,  will 
cause  a  slight  explosion. 

What  gas  is  set  free  by  the  action? 

Into  what  compound  is  the  tin  changed  ? 

Sn"  -f  2HC1  =  Sn"Cl2  +  2H. 
The  Sn  Cl*  is  stannous  chloride. 


TIN  AND    LEAD.  241 

It  is  easy  to  change  this  ous  chloride  into  the  ic  form 
just  as  ferrous  was  changed  into  ferric  chloride,  Ex.  157. 

Ex.  174-  —  Pour  about  2  cc.  of  the  SnCl2  solution  into 
another  tube,  add  four  or  five  drops  of  strong  nitric  acid, 
and  boil  the  mixture  a  minute. 

Is  there  any  evidence  of  a  chemical  change  ? 

But  we  may  go  further  and  prove  that  stannous  chloride 
is  no  longer  present,  in  this  way : 

Ex.  175.  —  Prepare  two  clean  tubes  with  10  cc.  of  water 
in  each,  and  add  to  one  about  a  cubic  centimeter  of  the 
solution  of  stannous  chloride  of  Ex.  173,  and  to  the  other 
about  as  much  of  the  solution  just  now  made.  Next  add, 
drop  by  drop,  a  solution  of  mercuric  chloride  to  the  first. 

What  is  the  color  of  the  precipitate  by  the  first  drop  ? 

What  change  occurs  when  more  and  more  are  added? 

These  are  the  changes  which  this  reagent  always  makes 
in  stannous  chloride.  Now  add,  to  the  other  solution, 
some  drops  of  mercuric  chloride  in  the  same  way.  No  such 
changes  should  take  place.  Then  it  is  plain  that  stannous 
chloride  is  not  present. 

The  fact  is  that  the  stannous  chloride  took' the  chlorine 
from  the  mercuric  chloride,  and  so  became  stannic  chloride. 
The  white  precipitate  at  first,  was  mercurous  chloride,  and 
the  gray  at  last,  was  mercury  itself.  Thus : 

1.  2HgCl2    +     SnCl2    =     SnCl4    +     Hg2Cl2 

Mercuric  Stannous  Stannic  Mercurous 

chloride  chloride  chloride  chloride 

2.  Hg2Cl2      +      SnCl2    =     SnCl4     +        Hg 

In  this  way  mercuric  chloride  will  always  tell  one 
whether  a  given  solution  of  a  compound  of  tin  is  stan- 
nous or  stannic  chloride. 

We  will  next  study  the  sulphides.  The  two  sulphides 
may  be  made  by  hydrogen  sulphide.  Thus : 


242  TIN   AND   LEAD. 

Ex.  176.  —  To  10  cc.  of  water  arid  £  cc.  of  the  stannous 
chloride  of  Ex.  173.  And  again,  to  10  cc.  of  water  add 
£  cc.  of  the  stannic  chloride  of  Ex.  174.  Then  pass  hydro- 
gen sulphide  through  both. 

The  first  gives  stannous  sulphide,  SnS,  brown. 

The  second  gives  stanic  sulphide,  SnS2,  lemon  yellow. 

It  is  plain  that  tin  must  be  added  to  the  list  of  metals 
whose  sulphides  are  insoluble  in  acid  water. 

Now  try  these  sulphides  with  yellow  Am2S.  Are  they 
soluble  in  it  ? 

Refer  back  to  antimony,  arsenic,  and  bismuth,  to  see 
which  of  these  have  sulphides,  which  behave  in  the  same 
way,  with  Am2S. 

LEAD.    PW. 

The  lead  ores  of  Spain  and  of  England  were  worked  by 
the  ancient  Romans,  and  still  farther  back,  even  before  the 
sacred  books  of  Exodus  and  Job  were  written,  this  metal 
was  known  and  used. 

The  ores  of  lead  are  many ;  but  for  the  most  part  they 
are  not  abundant.  One  of  them,  however,  is  found  in 
immense  beds  and  veins  in  the  rocks.  This  ore  is  called 
galena.  It  is  a  compound  of  lead  and  sulphur,  PbS.1 

Illinois,  Iowa,  and  Missouri,  to  say  nothing  of  several 
other  of  our  States,  have  an  abundance  of  galena  stored 
away  in  their  rocks. 

Extraction  of  Lead  from  its  Ores To  obtain  the 

metal,  the  ore  is  roasted,  on  the  floor  of  a  furnace,  with 
plenty  of  air.  The  hot  oxygen  changes  a  part  of  the  sul- 
phide into  sulphate  and  another  part  into  oxide,  while  a 
third  part  remains  as  it  was,  —  sulphide. 

The  furnace  is  then  shut  tight,  and  the  fire  driven  to  a 

1  The  symbol  for  lead,  Pb,  is  from  the  Latin  name  of  the  metal, 
Plumbum.  Lead  is  bivalent,  Pb  . 


TIN   AND    LEAD.  243 

greater  heat.  The  new  compounds,  just  mentioned,  then 
attack  and  decompose  each  other,  and  all  three  of  them 
give  up  their  metallic  lead.  The  way  in  which  these 
three  compounds  reduce  each  other  may  be  seen  by  writ- 
ing the  reactions.  The  three  substances  made  by  roasting 
are  PbS04,  Pb  0,  and  Pb  S. 

Then  Pb  S  O4  with  Pb  S  become  2  Pb  and  2  S  <)2 
and2PbO       "     PbS       »       3  Pb     »       SO, 

The  sulphurous  oxide  is  carried  away  by  the  draught, 
while  the  melted  lead  remains  covered  with  the  earthy 
impurities  of  the  ore,  —  a  melted  slag,  from  under  which  it 
may  be  drawn  off. 

BY  IRON.  —  There  is  another  way  of  getting  the  lead 
from  galena,  based  on  quite  another  principle.  In  fact  it 
may  be  given  to  illustrate  another  method  of  metallurgy, 
p.  194.  In  this  method  one  metal  is  used  to  liberate 
another.  This  is  called  the  precipitation  process. 

Some  lead  may  be  easily  obtained  by  "precipitation," 
and  the  experiment  will  illustrate  the  fact  that  one  metal 
may  displace  another  from  its  compounds.  Thus: 

Ex.  177.  —  Dissolve  8  g.  or  10  g.  of  lead  acetate,  com 
monly  called  "  sugar  of  lead,"  in  about  500  cc.,  a  pint  of 
water,  and  if  the  solution  is  cloudy  add  a  little 
acetic  acid  to  clear  it.  Put  this  into  a  white 
glass  bottle,  and  then  hang  in  it  a  strip  of 
clean  sheet  zinc  (Fig.  66),  and  let  it  stand 
undisturbed.  It  will  not  be  long  before  bril- 
liant crystals  of  lead  may  be  seen  on  the  sur- 
face of  the  zinc,  but  it  should  be  left  until 
to-morrow,  that  we  may  witness  the  beautiful 
growth  of  crystals,  which  has  long  been  called  the  lead-tree. 

Lead  acetate  and  zinc,  become  zinc  acetate  and  lead. 
This  shows  the  precipitation  of  a  metal  "  in  the  wet  way." 


244  TIN   AND    LEAD. 

But  in  the  case  of  lead  ores,  iron,  instead  of  zinc,  is 
used  to  liberate  the  lead,  and  the  change  is  brought  about 
by  heat  instead  of  in  solution.  The  ore  and  scraps  of  iron 
are  heated  together  in  a  blast-furnace,  when  the  iron  takes 
the  sulphur  away  from  the  lead,  thus  : 

Pb  S  +  Fe  =  Fe  S  +  Pb 

This  is  the  "precipitation"  of  a  metal  "by  heat." 

Properties  of  Lead — Lead  is  so  soft  as  to  be  easily 
cut  with  a  knife.  Its  freshly-cut  surface  shows  that  the 
metal  has  a  light-blue  color  and  a  line  luster,  which  may  be 
seen,  in  the  crystals,  in  Ex.  177.  It  is  a  heavy  metal,  being 
11.4  times  heavier  than  the  same  bulk  of  water. 

Its  attraction  for  moist  oxygen  is  quite  strong,  even  at 
common  temperatures,  so  that  its  surface  is  never  bright 
except  when  freshly  cleaned.  But  why  say  "  moist "  oxy- 
gen ?  Because  it  is  found  that  in  perfectly  dry  air  lead 
does  not  tarnish,  and  also  that  in  water  which  contains 
no  air  it  stays  bright,  which  shows  that  both  air  and 
moisture  are  required. 

Lead  Oxides.  —  Lead  combines  with  oxygen  to  make 
three  oxides.  When  heated  in  air  the  metal  is  changed  to 
lead  oxide,  PbO,  —  a  yellow  powder  known  as  litharye, 
which  is  used  in  making  flint-glass,  p.  185. 

There  is  also  the  lead  dioxide,  Pb02,  which  is  a  brown 
powder,  and  then  another  oxide,  Pb304,  called  minium,  or 
red  lead,  whicli  is  used  as  a  paint. 

Many  of  the  lead-salts  are  insoluble ;  in  fact,  the  nitrate 
and  the  acetate  are  the  only  two,  at  all  common,  which 
will  dissolve  in  water.  From  these  two,  the  student  can 
make  other  compounds  of  lead,  and  by  so  doing  become 
acquainted  with  the  chemical  actions  of  this  metal. 

Ex.  178.  —  To  make  the  carbonate.  First  make  a  dilute 
solution  of  lead  acetate,  and  make  it  clear  by  acetic  acid 


TIN   AND    LEAD.  245 

if  need  be,  but  use  just  as  little  acid  as  will  answer  this 
purpose.  Then  add  some  ammonium  carbonate.  The 
white  solid  obtained  is  "lead  carbonate." 

But  it  is  found  that  this  lead  carbonate  is  not  a  pure 
carbonate  ;  it  contains  lead  hydroxide  also.  It  is  often 
called  the  basic  carbonate.  This  basic  carbonate  is  the 
"  white  lead  "  which  is  so  much  used  as  a  paint. 

Salts  which  contain  an  hydroxide  are  called  basic  salts. 

Ex.  179.  —  To  a  dilute  solution  of  lead  nitrate *  add 
ammonium  hydroxide.  The  white  precipitate  is  not  a 
pure  hydroxide :  it  contains  lead  nitrate  also.  It  is  an- 
other basic  salt,  called  the  basic  nitrate. 

Of  what  other  metals  are  the  hydroxides  white  ? 

Is  this  lead  precipitate  soluble  or  insoluble  in  excess  ? 

What  other  hydroxides  are  like  it  in  this  respect? 

Ex.  180.  —  To  a  dilute  solution  of  lead  acetate  add  drops 
of  hydrochloric  acid.  No  precipitate  should  appear.  But 
now  use  hydrogen  sulphide.  The  black  precipitate  which 
falls  is  lead  sulphide,  PbS. 

What  other  metals  have  given  sulphides  by  H2  S  in  acid  ? 

Which  of  these  other  sulphides  does  this  lead  sulphide 
resemble  in  color  ? 

Will  Am2S  dissolve  this  lead  sulphide? 

Ex.  181.  —  To  a  strong  solution  of  lead  acetate  add  drops 
of  hydrochloric  acid.  A  white  precipitate  appears  :  it  is 
lead  chloride,  Pb  C12 .  Now  heat  the  mixture,  and  observe 
that  the  chloride  disappears.  Let  it  cool  again,  and  see 
that  the  chloride  returns  in  the  form  of  needle-shaped 
crystals.  Why  did  not  drops  of  HOI  make  a  precipitate 
of  this  chloride  in  Ex.  180,  as  well  as  in  this  one  ? 

All  this  proves  that  lead  chloride  is  somewhat  soluble 

1  Make  the  lead  nitrate  by  adding  drops  of  HNO8  to  the  basic 
carbonate  of  Ex.  178,  until  the  white  substance  is  dissolved. 


246  TIN   AND    LEAD. 

in  cold  water  (Ex.  180),  but  not  freely  (Ex.  181),  while  in 
hot  water  it  dissolves  largely  (Ex.  181). 

Have  we  found  any  other  metal,  so  far,  whose  chloride  is 
insoluble  ? 

If  a  solution  contains  either  Bi  or  Pb,  can  you  tell  which 
by  Ex.  181? 

If  a  solution  contains  Bi  or  Pb,  can  you  tell  which  by 
Ex.  180? 

Ex.  182.  —  To  a  moderately  strong  solution  of  lead 
nitrate  add  drops  of  potassium  iodide.  The  bright  yellow 
precipitate  is  lead  iodide,  which  is  very  sparingly  soluble 
in  the  cold. 

But  heat  the  mixture  and  the  iodide  disappears.  If 
there  is  water  enough  it  will  become  perfectly  clear.  Now 
let  the  tube  and  contents  cool,  and  watch  it. 

Describe  the  iodide  as  it  now  appears. 

Why  does  the  iodide  reappear? 

Lead  is  the  only  metal  whose  compounds  yield,  in  this 
way,  such  a  brilliant  and  crystalline  iodide.  Hence  this 
experiment  is  an  excellent  test  for  lead.  The  appearance 
of  rich  yellow  lead  chromate,  by  the  use  of  potassium 
chromate  (Ex.  163),  is  another  excellent  test  for  lead. 

QUERY.  —  By  what  experiments  could  you  decide  whether  a 
given  compound  is,  or  is  not,  a  compound  of  tin  or  lead? 
Try  it. 


THE    COPPER    GROUP. 

COPPER.    Cn". 

COPPER  is  often  found  in  nature  in  the  metallic  state. 
This  is  the  case  in  the  noted  copper-mines  of  Cornwall  and 
Devon,  in  England.  Some  of  the  finest  native  copper  in 
the  world  is  found  in  the  region  of  Lake  Superior,  where 
it  occurs  in  great  abundance.  One  single  mass,  of  Lake 
Superior  native  copper,  weighed  over  400  tons. 

Native  copper  is  crystalline.  The  separate  crystals  are 
usually  little  cubes,  but  in  some  cases  the 
cubes  are  grown  together  in  vast  numbers 
making  up  quite  large  masses,  and  these 
masses  often  show  most  singular  branch- 
like  forms,  sometimes  rudely  resembling 
the  form  of  some  growing  plant.  Fig.  67 
is  the  picture  of  a  specimen. 

But  copper,  as  native  metal,  is  much  less 
abundant  in  nature  than  are  its  ores. 

Copper  pyrites,  made  of  copper,1  iron  and 
sulphur,  CuFeS2,  is  the  ore  which  is  most 
common.  It  is  crystallized  in  cubes  of  per- 
fect form,  having  the  color  and  luster  of 
brass.  Besides  this  there  are  other  sulphides,  such  as 
Cu2  S  and  Cu  S,  also  found  in  considerable  quantity. 

Malachite  is  a  rich  ore  of  copper,  less  common  than 
pyrites.  It  is  a  green  stone,  which  takes  a  fine  polish,  and 
is  often  used  for  ornamental  purposes.  In  composition  it 

1  The  symbol  for  copper  is  Cu,  from  the  Latin  name  of  the  metal, 
Cuprum. 

247 


248  THE    COPPER    GROUP. 

is  a  basic  carbonate,  for  it  contains  both  the  carbonate  and 
the  hydroxide  of  copper,  CuC  03,  Cu  (H  0)2. 

Other  ores  of  copper  are  widely  distributed.  Some  are 
blue,  some  are  red,  some  are  purple,  some  are  gray,  but  we 
need  not  stop  to  describe  them. 

Extraction  of  Copper.  — The  metal  is  extracted  from 
its  sulphide  by  roasting  and  reducing  it  in  air.  The  ore 
is  first  roasted  and  then  melted,  and  then  roasted  again ; 
this  changes  a  part  of  the  sulphide  into  copper  oxide,  Cu  0. 
This  roasted  ore  is  then  mixed  with  sand  and  heated  in 
a  reverberatory  furnace.  The  copper  goes  back  into  the 
form  of  sulphide  while  the  iron  of  the  ore  takes  oxygen, 
and,  with  the  sand,  becomes  a  liquid  silicate.  At  the  end 
of  this  repeated  roasting  the  copper  is  still  combined  with 
sulphur,  but  it  is  rid  of  the  iron. 

The  rest  of  the  operation  is  like  that  of  getting  lead. 
The  sulphide  is  again  roasted ;  a  part  of  it  is  changed  to 
oxide,  while  the  rest  remains  as  sulphide,  and  then,  by 
heating  them  strongly,  these  two  compounds  attack  each 
other,  and  the  copper  of  both  is  set  free.  Thus  : 
Cu,S  +  2CuO  =  4Cu  +  S02 

Properties.  —  This  metal  has  a  peculiar  deep  red  color, 
not  to  be  seen  in  any  other.  It  is  rather  soft,  easily  bent, 
very  ductile,  and  very  strong.  It  is  one  of  the  very  best 
conductors,  and  this  makes  copper,  more  than  any  other 
metal,  useful  in  all  the  applications  of  electricity. 

^jloys.  —  The  alloys  of  copper  are  many  and  important. 
Brass  is  an  alloy  of  copper  and  zinc ;  German  silver,  of  cop- 
per, zinc,  and  nickel ;  while  bronze,  and  bell-metal,  and  gun- 
metal,  are  made  of  different  proportions  of  copper  and  tin. 

Copper  Compounds.  —  Copper,  when  long  exposed  to 
moist  air,  turns  green ;  the  green  coating  is  a  carbonate. 
The  metal  does  not  unite  with  oxygen  at  common  temper- 
atures of  the  air,  but  when  heatecj.  it  does,  and  if  intensely 


THE    COPPER    GROUP.  249 

heated,  it  slowly  burns,  giving  a  fine  green  color  to  the  flame 
which  heats  it.  This  may  be  easily  shown  by  holding  a 
small  copper  wire  for  some  time  in  the  edge  of  the  Bunsen 
flame.  There  are  two  oxides  of  copper  :  one  is  the  cuprous 
oxide,  Ciu  0,  which  is  red ;  the  other  is  the  cupric  oxide, 
Cu  0,  which  is  black.  So  there  are  also  two  chlorides,  two 
iodides,  two  sulphides,  and,  in  fact,  two  classes  of  copper 
compounds,  the  cuproz«s  and  the  cupr/c. 

Cupric  Sulphate.  —  The  cupric  sulphate  is  the  most 
common  salt  of  this  metal.  It  is  usually  called  copper 
sulphate.  It  comes  in  the  form  of  blue  crystals,  Cu  S  04  + 
5  H2  0.  The  blue  color  depends  upon  the  water  of  crystal- 
lization, for  when  the  water,  5  M2  0,  is  driven  off  by  heat, 
as  it  may  be  very  easily,  the  substance  is  white.  This 
salt  goes  under  the  common  name  of  "blue  vitriol,"  just 
as  the  ferrous  sulphate  is  called  "green  vitriol,"  and  as  the 
zinc  sulphate  is  called  "white  vitriol." 

Study  of  Some  Reactions  of  Copper.  —  Starting  with 
the  copper  sulphate  the  student  can  produce  several  of  the 
compounds  of  copper,  and  in  this  way  become  acquainted 
with  some  of  the  chemical  peculiarities  of  this  metal. 

Ex.  183.  —  Reduce  a  little  copper  sulphate  to  powder 
and  dissolve  it  in  water  little  by  little.  First  see  how  little 
will  be  needed  to  give  a  perceptible  blue  color  to,  say  10  cc. 
of  cold  water  in  a  tube.  Then  add  more  and  more  until 
it  no  longer  disappears  when  shaken. 

Many  other  copper  compounds  in  solution  have  the  same 
color  as  this  one.  Indeed,  when  this  blue  color  is  seen  in 
a  liquid  it  is  a  sign  of  the  presence  of  some  copper  corn-- 
pound, —  not  a  proof,  but  a  sign.  This  solution  may  be  used 
for  the  experiments  which  follow. 

Ex.  184-  —  Add  a  cubic  centimeter  of  the  copper  sulphate 
solution  to  10  cc.  of  water.  Into  this  put  slowly,  one,  two, 


250  THE    COPPER    GROUP. 

three  drops  of  ammonium  hydroxide,  arid  shake  it  well. 
The  precipitate,  which  is  deep  blue  when  just  enough  of 
the  reagent  is  used,  is  copper  hydroxide,  Cu  (H  O)2.  With 
too  little  reagent  the  precipitate  is  pale  blue. 

Is  this  hydroxide  soluble  in  excess  ? 
Compare    this    result  with   the    effect   of  ammonia   on 
zinc,  nickel,  and  cobalt,  hydroxides. 

Compare  it  also  with  lead  and  bismuth  hydroxides. 

Ex.  185.  —  Add  a  cubic  centimeter  of  the  copper  sulphate 
solution  to  10  cc.  of  water,  and  a  few  drops  of  hydrochloric 
acid. 

Note  the  evidence  that  copper  chloride  is  soluble. 
Then  add  hydrogen  sulphide  :  black  Cu  S  is  made. 

What  other  metals  have  given  sulphides  in  acid  water  ? 
Which  of  those  others  does  this  Cu  S  most  resemble  ? 
Find  out  whether  it  is  soluble  or  insoluble  in  Am2S. 

The  same  brown-black  sulphide  is  made  when  Am2S  is 
added  directly  to  the  original  solution  of  cupric  sulphate  : 


CuS04  +  (NH4)aS  =  CuS  +  (NH4),S04 

and  ammonium  sulphate  (XH4)2S04  is  also  made,  which 
remains  dissolved. 

Ex.  186.  —  Place  a  bright  piece  of  iron  wire,  or  a  knife- 
blade,  in  a  dilute  solution  of  copper  sulphate  in  water: 
it  is  soon  coated  with  red  metallic  copper.  Leave  it  in 
until  the  blue  color  is  all  gone  from  the  liquid.  Then  try 
a  fresh  piece  of  bright  iron.  It  will  need  some  time,  but 
the  iron  will  take  every  particle  of  copper  out,  so  that 
this  fresh  piece  will  not  be  coated  at  all. 

Cu  S  O4  +  Fe  =  Cu  +  Fe  S  O4 
Now  by  this  reaction  we  see  that,  besides  the  metallic 


THE    COPPER    GROUP.  251 

copper,  Cu,  some  ferrous  sulphate,  l\jS04,.must  be  made 
at  the  same  time. 

Does  the  color  of  the  liquid  suggest  the  presence  of  an 
iron  compound  ?  See  Ex.  155. 

Can  you  prove,  by  experiment,  that  it  does  contain  iron  ? 

MERCURY.    Hg". 

Mercury  l  is  sometimes  found  in  the  earth  as  native 
metal,  but  oftener  in  combination  with  sulphur.  The  sul- 
phide, Hg  S,  is  its  chief  ore,  and  it  is  called  cinnabar.  The 
color  of  this  ore  is  dark  red,  and  in  some  specimens  it  is 
almost  as  rich  and  brilliant  as  vermilion.  Indeed,  these 
two  things  have  the  same  composition ;  cinnabar  is  the 
native  sulphide,  vermilion  is  the  artificial  sulphide.  The 
ore  is  found  in  many  countries;  Spain,  Austria,  China, 
and  California  are  examples. 

Extraction  of  the  Metal Mercury  is  easily  obtained 

from  cinnabar.  The  ore  only  needs  to  be  roasted,  when 
this  reaction  will  occur : 

HgS-f  20  =  Hg  +  S02 

The  ore  is  decomposed  by  the  hot  air ;  its  sulphur  burns 
off  as  sulphurous  oxide,  while  its  mercury  is  left  free. 
The  metal  is  then  in  the  form  of  vapor,  which  is  led  into 
cold  vessels,  where  it  becomes  liquid. 

PROPERTIES.  —  Mercury  is  a  liquid,  —  the  only  liquid 
metal.  It  is  tin-white,  with  a  splendid  luster.  It  is  very 
heavy,  —  thirteen  and  a  half  times  heavier  than  the  same 
volume  of  water.  When  cooled  down  to  — 39.5°  C.  it  freezes 
to  a  white  lustrous  solid ;  when  heated  to  350°  C.  it  boils. 

With  some  other  metals  it  makes  alloys,  but  the  alloys 
of  mercury  are  generally  called  amalgams.  Zinc,  copper, 

1  The  symbol  for  mercury,  Hg,  is  taken  from  the  Latin  Hydrar- 
gyrum, 


252  THE    COPPER    GROUP. 

silver,  and  gold  are  changed  into  amalgams  at  once  by 
contact  with  mercury. 

Compounds  of  Mercury Mercury  does  not  tarnish 

in  air  unless  heated,  but  if  kept  at  almost  boiling  heat, 
it  is  changed  into  mercuric  oxide,  HgO,  known  as  the 
"  red  oxide,  "  Ex.  5.  This  metal  also  forms  two  series  of 
compounds,  the  -lc  and  the  ous.  Thus  we  find  mercuric 
chloride  and  mercurous  chloride,  mercuric  and  mercurous 
sulphates. 

Mercuric  chloride,  Hg  C12 ,  is  the  virulent  poison,  known 
under  the  name  of  corrosive  sublimate. 

Mercurous  chloride,  Hg.2Cl2,  is  the  medicine  known 
under  the  name  of  calomel. 

Both  of  these  are  white  solids,  and  when  seen  in  powder 
are  alike  in  appearance,  but  the  poison  is  soluble  in  water, 
while  the  medicine  is  insoluble. 

MERCUROUS  COMPOUNDS. — The  metal  mercury  is  soluble 
in  nitric  acid,  which,  if  dilute,  changes  it  to  mercurous 
nitrate. 

Ex.  187.  —  Put  a  small  globule  of  mercury  into  a  tube, 
and  add  a  cubic  centimeter  of  dilute  nitric  acid.  Then 
heat  it.  The  mercury  will  slowly  waste  away,  and,  if  need 
be,  let  more  acid  be  added,  but  not  too  much,  so  that 
the  metal  shall  be  completely  dissolved. 

This  solution  of  mercurous  nitrate  may  be  used  as 
follows :  — 

Ex.  188.  —  Add  a  few  drops  of  it  to  5  cc.  of  water,  and 
then  add  drops  of  hydrochloric  acid.  The  white  solid 
obtained  is  mercurous  chloride,  or  calomel,  Hg2Cl2. 

What  other  metal  yields  a  precipitate  with  H  Cl? 

Is  this  chloride,  like  that  one,  soluble  by  boiling  ? 

Now  add  to  the  white  chloride  a  little  ammonium 
hydroxide  and  note  the  marked  change  in  color.  This  is 


THE    COPPER    CROUP.  253 

the  only  white  chloride  which  will  turn  black  when 
treated  with  ammonia. 

Ex.  189.  —  Add  a  few  drops  of  the  nitrate  to  5  cc.  water, 
and  then  add  ammonium  hydroxide.  The  same  black 
precipitate  is  made  at  once. 

Mercurous  compounds  are  the  only  ones  which  yield 
black  precipitates  with  ammonia. 

MERCURIC  COMPOUNDS.  —  A  solution  of  corrosive  subli- 
mate, mercuric  chloride,  may  be  the  starting-point  in  our 
study  of  the  chemical  actions  of  mercuric  compounds. 

Ex.  190.  —  Add  a  cubic  centimeter  of  mercuric  chloride 
to  5cc.  of  water.  Add  also  drops  of  hydrochloric  acid. 
No  precipitate  will  appear. 

Can  you  explain  the  fact  that  H  Cl  can  make  no  precipi- 
tate in  any  mercuric  compound  ? 

Finally  add  hydrogen  sulphide,  and  notice  any  changes 
of  color  which  may  occur.  At  first  the  precipitate  may 
be  white,  but  with  more  and  more  H2  S  it  'will  become 
yellow,  brown,  and  at  last  black.  The  mercuric  sulphide, 
HgS,  when  well  formed  is  black. 

What  other  metals  have  given  black  sulphides  by  H2  S  ? 

Ex.  191.  —  Add  a  cubic  centimeter  of  Hg  C12  to  5  cc.  of 
water,  and  then  use  NH4HO,  little  by  little,  to  excess. 

What  is  the  difference  between  the  actions  of  1ST  H4  H  0 
on  the  mercurous  and  the  mercuric  compounds? 

Ex.  192. — To  another  dilute  solution  of  the  HgCl2  add 
one  drop  of  hydrochloric  acid,  and  then  put  into  it  a 
piece  of  bright  copper  wire. 

Notice  the  coating  which  soon  gathers  on  the  wire. 

What  is  it  ?  Its  appearance,  especially  when  rubbed, 
will  be  likely  to  inform  you.  So  will  the  reaction  if  it 
Ire  written,  thus: 

Hg. 


254  THE    COPPER    GROUP. 


SILVER.    AS*. 

Silver  is  sometimes  found  in  the  native  state.  Such 
specimens  are  often  very  beautiful,  looking  like  metallic 
twigs  and  branches.  But  this  metal  is  more  abundant  in 
combination,  sometimes  with  chlorine,  but  oftener  with 
sulphur.  The  sulphide  of  silver  is  sometimes  found  alone, 
but,  in  most  cases,  it  is  in  company  with  the  sulphides  of 
other  metals,  such  as  lead  and  copper.  These  mixed 
sulphides  of  silver  and  other  metals  are  the  chief  ores  of 
silver. 

Silver  is  almost  always  present  in  galena,  and  much 
silver  is  obtained  from  that  ore. 

Extraction  of  the  Metal.  —  There  are  different  'ways 
of  taking  silver  from  its  ores.  We  will  study  two  of 
these. 

First  suppose  the  silver  is  to  be  taken  from  its  sulphide, 
which  contains  the  sulphides  of  other  metals,  as  it  usually 
does.  Can  the  ore  be  treated  the  same  as  the  ores  of 
zinc  or  lead,  —  that  is,  changed  to  an  oxide  by  roasting 
in  air  ?  No,  because  silver,  unlike  those  metals,  has  very 
little  attraction  for  oxygen.  But  it  has  a  very  strong 
attraction  for  chlorine,  and  this  fact  is  made  use  of  to 
get  the  metal  away  from  the  sulphur  in  its  ore. 

For  this  purpose,  the  ore  is  well  stamped,  to  crush  it 
to  powder,  and  then  mixed  with  a  little  —  about  one 
tenth  its  weight,  common  salt  —  sodium  chloride.  The 
mixture  is  then  heated,  and,  to  make  sure  that  the  work 
is  well  done,  the  ore  is  mixed  with  more  salt  and  heated 
again.  In  this  operation,  the  chlorine  of  the  salt  seizes 
the  silver  of  the  ore,  and  holds  it  in  the  form  of  silver 
chloride. 

The  next  thing  is  to  take  the  chlorine  away,  and  iron 
is  used  for  this  purpose  because  chlorine  has  a  stronger 


THE    COPPER    GROUP.  255 

attraction  for  iron  than  for  silver.  The  chloride  of  silver 
is  put  into  strong  oaken  casks,  with  a  little  water  and 
fragments  of  iron.  This  mixture  is  violently  shaken  by 
turning  the  casks  rapidly,  and,  under  this  treatment,  the 
iron  robs  the  silver  of  its  chlorine.  The  silver  is  thus 
left  free,  but  it  is  in  very  fine  particles  scattered  through 
the  mixture  in  the  casks.  How  shall  it  be  collected? 

Just  at  this  point  the  use  of  mercury  comes  in.  Mercury 
is  poured  into  the  casks,  which  are  then  set  rotating  again 
faster  than  before.  This  brings  the  silver  and  mercury 
together,  and  they  at  once  combine  to  form  an  amalgam, 
p.  251,  and  the  next  thing  is  to  get  the  silver  out  of  this 
amalgam. 

To  do  this  it  is  only  necessary  to  heat  the  amalgam, 
when  the  mercury  will  pass  off  as  vapor  while  the  silver 
will  be  left  behind. 

But  the  metal  is  still  mixed  with  such  other  metals,  — 
copper,  iron,  and  antimony,  as  were  in  the  ore.  These  must 
be  removed,  and  so  the  metal  is  mixed  with  lead,  and  again 
melted  while  a  current  of  air  is  driven  over  its  surface. 
The  oxygen  seizes  the  lead  and  other  metals,  but  not  the 
silver,  which  is  thus  left  pure. 

SILVER  FROM  GALEXA.  —  But  much  of  the  silver  now 
in  use  comes  from  the  lead  ore,  galena.  When  the  lead 
is  obtained  from  this  ore  by  the  method  described,  p.  242, 
the  silver  comes  with  it,  and  then  the  problem  is,  how  to 
get  the  small  quantity  of  silver  out  of  the  large  mass  of 
lead. 

The  lead  is  melted,  and  then  allowed  to  slowly  become 
cold.  When  it  cools,  crystals  begin  to  form,  and  these 
crystals  are  pure  lead.  These  crystals  of  lead  are  taken 
out  with  a  strainer.  They  are  melted  over  again,  and 
again  cooled;  another  crop  of  pure  lead  crystals  is  then 
taken  out,  and  this  heating,  and  cooling,  and  dipping  out 


256  THE    COPPER    GROUP. 

pure  lead  is  continued,  the  silver  every  time  remaining  in 
the  molten  mass,  until  what  is  left  behind  is  quite  rich 
in  the  precious  metal. 

And  then  oxygen  is  called  upon  to  take  away  the  lead 
that  remains.  The  rich  alloy  is  melted  on  a  bed  of  bone- 
ash,  and  hot  air  is  driven  over  it.  The  hot  oxygen  seizes 
the  lead,  but  does  not  combine  with  the  silver.  The  lead 
oxide  soaks  into  the  porous  bone-ash  and  leaves  the  pure 
silver  behind.  This  method  of  separating  silver  from  lead 
is  called  cupellation. 

Properties  of  Silver.  —  Silver  is  the  whitest  of  metals. 
It  is  ten  and  a  half  times  as  heavy  as  water.  It  is  much 
harder  than  gold,  and  very  malleable  and  ductile. 

Oxygen  does  not  attack  it  even  when  hot ;  but  its  surface 
will  quickly  blacken  in  the  presence  of  hydrogen  sulphide 
because  silver  and  sulphur  strongly  attract  each  other. 

Articles  of  silver-ware  and  silver  coin  are  well  known. 
But  we  must  remember  that  none  of  these  are  made  of  pure 
silver.  The  pure  metal  is  quite  too  soft  to  be  able  to  stand 
the  wear  which  these  things  receive.  To  harden  the  silver, 
small  portions  of  other  metals  are  mixed  with  it. 

For  silver  coin,  some  copper  is  added  to  harden  the 
precious  metal.  In  this  country  the  standard  coin  metal  is 
made  of  silver  90  parts  and  copper  10  parts.  In  England 
the  proportion  of  copper  is  less  (7.5),  in  Germany  it  is 
more  (12.5). 

Compounds  of  Silver The  most  important  com- 
pound of  silver1  is  the  nitrate,  AgNO3,  and  this  is  made 
by  the  action  of  nitric  acid  on  the  metal.  This  action 
begins  instantly  on  putting  the  two  together,  and  goes 
on  vigorously  until  one  or  the  other  is  exhausted. 

1.  Ag    +    HN08    =    AgN08    +      H 

2.  H      +    HN08    =       H20       +    NO, 

1  The  symbol  for  silver  is  Ag,  from  the  Latin  name  Argenlum. 


THE    COPPER    GROUP.  257 

The  silver  takes  the  place  of  hydrogen  in  the  acid, 
making  the  silver  nitrate,  Ag  N  03 ,  and  setting  the  hydro- 
gen free,  but  this  hydrogen  instantly  attacks  another  por- 
tion of  nitric  acid,  and  forms  water  and  nitrogen  dioxide. 
The  liquid  left  is  a  solution  of  silver  nitrate.  By  evapo- 
rating this  liquid,  transparent  crystals  of  the  silver  nitrate 
may  be  obtained. 

Ex.  193.  —  To  10  cc.  of  water  add  4  or  5  drops  of  silver 
nitrate,  and  then  add  drops  of  hydrochloric  acid.  A  white 
precipitate  forms  at  once :  what  is  it  ? 

Boil  this  precipitate,  as  lead  chloride  was  boiled  in  Ex. 
181.  Is  it  soluble  in  hot  water,  like  lead  chloride  ? 

Add  ammonium  hydroxide  to  it,  as  was  done  with  the 
Hiercuro^s  chloride,  Ex.  189. 

Does  it  blacken  by  ammonia,  as  the  mercurous  chloride 
did  ?  What  is  the  effect  of  the  ammonia  on  it  ? 

By  these  differences,  we  can  easily  distinguish  these 
three  chlorides,  one  from  another. 

Ex.  194.  —  To  10  cc.  water  add  drops  of  silver  nitrate, 
and  then  hydrochloric  acid,  or  a  solution  of  common  salt, 
which  will  have  the  same  effect.  Place  the  tube  with  this 
white  silver  chloride  in  sunlight,  and  notice  its  change 
of  color. 

Other  silver  salts  are  also  very  sensitive  to  the  action 
of  light.  On  this  account  the  compounds  of  silver  are 
much  used  in  the  art  of  photography. 

Separation  of  Silver  and  Copper.  —  We  have  seen 
that  silver  coin  is  an  alloy  of  silver  and  copper.  The  two 
metals  have  been  melted  together :  can  we  get  them  apart 
again,  or  prove  that  they  are  in  the  coin?  The  student 
is  now  able  to  do  this,  and  the  work  is  an  interesting  and 
instructive  exercise. 

Ex.  195.  —  Put  a  ten-cent  piece  in  an  evaporating-dish 
and  cover  it  with  a  mixture  of  strong  nitric  acid  and  water, 


258  THE    COPPER    GROUP. 

half  and  half.  Then  heat  gently,  until  chemical  action 
begins.  Describe  the  action,  thus  : 

What  gas  is  set  free?  What  color  does  the  liquid 
become  ? 

What  compound  of  silver  is  made  ?  What  compound  of 
copper  ? 

When  the  chemical  action  is  over,  or  nearly  so,  pour 
about  1  cc.  of  the  blue  liquid  into  about  5  cc.  of  water,  and 
then  add  drops  of  hydrochloric  acid,  or,  better,  of  solution 
of  common  salt,  NaCl,  until  a  drop  no  longer  makes  a 
precipitate.  Let  the  precipitate  settle,  and  then  pour  the 
liquid  off  into  another  tube. 

Wash  the  precipitate  by  pouring  water  upon  it,  shaking, 
and  then,  when  it  is  settled  again,  pouring  the 'water  off 
into  the  waste.  Do  this  a  second  time. 

Now  you  have  the  copper  of  the  coin  in  the  blue  liquid, 
and  the  silver  of  the  coin  in  the  white  precipitate. 

Prove  that  the  blue  liquid  contains  copper,  by  the  use  of 
iron,  Ex.  186. 

Prove  that  the  white  precipitate  is  silver  chloride  by 
treating  a  part  of  it  with  hot  water,  another  part  with 
ammonia,  and  exposing  another  part  to  the  sunlight. 

SUGGESTION.  —  Take  specimens  from  the  teacher  or  a  friend 
who  knows  what  they  are,  and,  by  experiment,  decide  whether 
each  one  is,  or  is  not,  a  compound  of  lead,  of  silver,  or  of  mer- 
cury. If  it  prove  to  be  a  compound  of  mercury,  then  decide 
whether  it  is  a  mercuric  or  mercurous  compound. 


GOLD    AND    PLATINUM. 

GOLD.    Au"r. 

GOLD  is  almost  always  found  in  the  native  state.  Unlike 
the  metals  described  before,  this  precious  metal  is  very 
rarely  found  in  combination  with  other  elements  :  it  is 
found  as  native  metal.  Yet  this  native  gold  is  not  pure ; 
it  is  mixed  with  silver,  and  sometimes,  too,  with  copper, 
and  often  with  other  baser  metals.  Native  gold  is  found 
in  fine  grains  among  the  sands  of  certain  rivers,  and  also 
in  solid  quartz  rocks.  Now  and  then  a  nugget  of  consid- 
erable size  occurs. 

Extraction  of  Gold.  —  Gold  is  obtained  from  sands  and 
other  loose  materials  by  the  process  called  "washing." 
The  material  is  put  into  a  shallow  pan  and  well  stirred  up 
with  water.  Gold  is  so  heavy  that  the  grains  will  quickly 
settle  to  the  bottom,  and  then  the  earthy  matter  may  be 
poured  off  from  above  it.  Sometimes  the  gold-bearing 
deposit  is  washed  by  rocking  it  in  a  cradle  through  which 
a  stream  of  water  is  slowly  running.  The  lighter  earth 
or  sand  is  then  washed  away,  while  the  heavy  gold  dust 
lags  behind,  and  is  caught  in  grooves  in  the  bottom  of 
the  cradle.  The  precious  metal  is  then  dissolved  in  mer- 
cury, and  afterward  separated  by  heat. 

Gold  is  obtained  from  quartz  rock  by  "  amalgamation." 
The  quartz  rocks  are  crushed  to  the  finest  powder  and 
then  mixed  with  mercury.  The  mercury  dissolves  the 
gold  and  leaves  the  quartz.  The  amalgam  of  gold  is  then 
distilled,  and  the  mercury  goes  away  as  vapor  while  the 
gold  is  left  behind. 

PROPERTIES.  —  Gold  is  remarkable  for  its  fine  yellow 
color  and  beautiful  luster.  It  is  among  the  heaviest  of 

259 


2 GO  GOLD    AND    PLATINUM. 

metals,  about  nineteen  times  (19.33)  heavier  than  water. 
It  is  the  most  malleable  of  metals ;  it  is  said  that  leaves 
have  been  beaten  so  thin  that  280,000  would  be  needed 
to  make  an  inch  in  thickness !  There  is  a  curious  fact 
about  the  color  of  gold-leaf ;  it  is  this :  looked  at  in  the 
usual  way  it  is  yellow,  but  let  a  leaf  be  spread  upon  glass, 
so  that  it  may  be  held  up  between  the  eye  and  a  window, 
or  the  sky,  and  it  will  be  green. 

At  a  temperature  of  about  2000°  F.  (1102°  C.)  this  pre- 
cious metal  melts  into  a  greenish-colored  liquid.  The 
highest  heat  of  a  furnace  can  scarcely  change  it  into 
vapor,  but  the  furious  flame  of  the  oxyhydrogen  blowpipe 
can;  its  vapor  has  a  purple  hue. 

Few  chemicals,  even  of  the  most  corrosive  character, 
<3an  harm  this  noble  metal.  Oxygen  cannot  rust  it ; 
sulphur  cannot  tarnish  it ;  nor  can  the  strongest  acids 
corrode  it.  For  one  element,  however,  it  has  a  strong 
attraction;  this  is  chlorine.  On  this  account  it  dissolves 
readily  in  aqua  regia ;  in  fact  this  liquid  received  its 
name,  which  means  royal  water,  because  it  was  found  to 
dissolve  gold,  the  "king  of  metals."  It  changes  the 
gold  to  gold  chloride,  AuClg.1 

Gold  is  used  for  ornament  and  as  money.  But  when 
pure  it  is  almost  as  soft  as  lead,  and  hence  unfit  for 
either  use.  To  make  it  harder  a  little  copper  or  silver 
is  added.  The  alloy  used  for  coin  in  this  country  must 
be  made  of  nine  parts  of  gold  to  one  part  of  copper. 

PLATINUM.    Pt. 

Platinum  is  a  still  rarer  metal  than  gold.  In  small 
quantities  gold  is  very  widely  distributed  in  the  earth, 
but  platinum  is  found  in  few  places.  It  is  found  in 
largest  quantity  on  the  slopes  of  the  Ural  mountains,  and 

1  The  symbol  for  gold  is  Au,  from  the  Latin  Aurum. 


GOLD    AND    PLATINUM.  261 

in  Brazil  arid  Peru.  It  is  always  found  in  the  native  state, 
but  mixed  with  other  metals,  several  of  which,  like  osmium 
and  iridium,  are  still  rarer  metals  than  itself. 

Pure  platinum  is  silver-white.  Oxygen  cannot  attack 
it  at  any  temperature,  and  only  the  intense  heat  of  the 
blowpipe  can  melt  it.  On  these  accounts  platinum  vessels 
are  much  used  in  the  laboratory.  Aqua  regia  and  the 
caustic  alkalies  will  dissolve  platinum,  and  many  other 
metals  will  form  alloys  with  it,  which  melt  more  easily 
than  the  metal  itself  and  are  attacked  by  acids. 

The  Platinum  Group —  There  are  five  very  rare  metals 
which  are  much  like  platinum  in  many  of  their  properties. 
They  are  palladium,  iridium,  osmium,  ruthenium,  and 
rhodium.  Palladium  is  remarkable  for  its  action  on  hy- 
drogen. When  heated  to  redness  it  absorbs  this  gas,  and 
forms  what  seems  to  be  a  true  alloy.  And  this  fact  would 
indicate  that  hydrogen  is  itself  a  metal.  Accordingly  it  is 
sometimes  called  hydrogenium. 

Osmium  is  remarkable  for  its  great  weight ;  it  is  the 
heaviest  substance  known,  having  a  specific  gravity  of 
22.477.  An  alloy  of  osmium  and  iridium  is  found  some- 
times in  the  sands  with  gold ;  it  is  harder  than  steel,  and 
is  used  for  the  tips  of  gold  pens. 


CLASSIFICATION    OF    THE    METALS. 

How  Classes  are  made.  —  We  have  seen  that  some 
elements  combine  with  oxygen  and  hydrogen  to  produce 
acids  while  others  combine  with  oxygen  and  hydrogen  to 
produce  bases.  If  we  put  all  those  which  produce  acids 
together,  and  all  those  which  produce  bases  together,  we 
have  all  the  elements  in  two  large  groups,  —  the  non- 
metals  and  the  metals. 

Now  this  illustrates  the  way  in  which  classes  are  made. 
If  the  chemist  has  a  large  number  of  substances,  he  may 
find,  by  studying  them  separately,  that  several  are  alike 
in  some  important  character;  these  he  can  put  together 
to  form  a  class  or  group.  Others  in  the  list  will  not  agree 
with  these,  but  while  unlike  them  they  will  be  like  one 
another,  and  these  he  can  put  together  to  form  a  second 
class  or  group.  And  in  this  way  he  may  at  length  have 
the  entire  list  divided  into  groups,  —  each  group  holding 
only  those  individuals  which  are  alike  in  the  leading  char- 
acter, however  much  they  may  differ  in  other  particulars. 

THE  CLASSES  OF  NON-METALS.  —  We  have  seen  that 
the  non-metals  are  placed  in  four  groups,  known  as  the 
chlorine  group,  the  sulphur  group,  the  nitrogen  group, 
and  the  carbon  group.  The  leading  character,  or,  we  may 
say,  the  foundation  of  this  grouping,  is  valence.  All  uni- 
valent  non-metals  are  put  into  one  group,  all  bivalent 
non-metals  into  another,  all  trivalent  non-metals  into  a 
third,  and  the  quadrivalent  non-metals  into  a  fourth. 

THE  METALS  NOT  CLASSED  IN  THE  SAME  WAY.  —  Now 
the  classification  of  the  metals  is  also  sometimes  founded 
on  valence.  Then,  all  univalent  metals  go  together  into 
one  group,  all  bivalent  into  another,  and  so  on.  But  in 

262 


CLASSIFICATION.  263 

this  book,  the  metals  have  not  been  grouped  in  this  way, 
and  the  reason  is,  simply,  that  such  groups  of  the  metals 
would  not  best  suit  our  particular  purpose  in  the  study  of 
these  elements.  What  we  have  wanted  to  do  is  to  become 
acquainted  with  the  general  properties  and  behavior  of  the 
metals,  and  if  they  are  grouped  by  their  valence,  metals 
quite  different  in  properties  and  actions  will  sometimes 
be  thrown  together.  As,  for  instance,  silver  is  univalent, 
so  are  potassium  and  sodium,  and  all  these  will  be  in  the 
univalent  group  if  our  classes  are  made  by  valence. 
But  silver  has  few  properties  like  the  others.  If  we  are 
studying  the  properties  of  the  metals,  it  is  better  to  put 
those  together  which  are  most  nearly  alike,  and  then  silver 
will  go  with  copper  and  mercury,  instead  of  with  potassium 
and  sodium. 

MORE  THAN  ONE  WAY  TO  GROUP  THEM.  —  In  fact,  the 
classes  of  metals  in  this  book  are  founded  on  likeness  of 
properties,  and  not  on  valence.  Thus  we  have  the  potas- 
sium group,  because  there  are  several  metals  which  are 
all  very  much  like  potassium,  —  soft,  light,  alkaline ;  and 
the  calcium  group,  because  there  are  several  metals  like 
calcium ;  and  the  iron  group,  because  the  properties  of 
iron  are  much  the  same  as  those  of  the  other  members. 
This  is  the  most  helpful  way  of  grouping  the  metals 
when  our  object  is  to  study  their  properties. 

But  there  must  be  some  reason  why  some  elements  are 
so  much  alike  and  others  so  different.  There  must  be 
some  reason  why  some  are  univalent,  others  bivalent,  and 
others  with  still  different  degrees  of  valence.  If  we  could 
only  get  at  this  cause  of  their  differences,  the  elements 
would  fall  into  natural  groups.  We  could  then  know  the 
place  of  every  one  of  them  in  the  true  system  of  nature. 
But  the  chemist  does  not  yet  know  this  cause.  He  knows 
the  facts  only.  On  this  account  the  true  system  of  the 


264  CLA.^.^lFK  ATIOX. 


elements  in  nature  is  still  beyond  his  reach.  And  until 
he  reaches  it,  the  elements  will  be  classified  in  different 
ways,  as  different  leading  facts  are  chosen  on  which  the 
classes  may  be  founded. 

FOUR  WAYS  TO  CLASSIFY  THE  METALS.  —  There  are,  in 
fact,  four  important  ways  of  classifying  the  metals.  One 
way  is  founded  on  valence;  a  second  way  is  founded  on 
likeness  of  pi^erties  ;  a  third  way  is  founded  on  atomic 
weights  ;  a  fourth  way  is  founded  on  the  solubility  of  com- 


We  need  not  stop  longer  with  the  first  two  of  these; 
the  third  and  fourth  are  yet  to  be  described.  The  third 
is  important  because  it  includes  all  elements,  metals  and 
non-metals  alike,  in  one  system,  and  comes  nearer  than 
any  other  to  being  the  "  natural "  system.  The  fourth 
is  important  because  it  is  used  in  chemical  analysis. 

THE    NATURAL    SYSTEM. 

Classification  by  Atomic  Weights —  We  have  seen 
that  the  elements  chlorine,  bromine,  iodine,  and  fluorine 
are  very  much  alike  in  properties.  They  also  combine  with 
the  same  elements  and  in  the  same  proportions.  But  while 
they  have  many  of  the  same  properties  they  have  them  in 
different  degrees.  Fluorine  is  the  most  active,  chlorine 
next,  then  bromine,  and  finally  iodine  is  least  active  of 
all.  Their  properties  vary  in  this  order.  .And  we  have 
also  noticed  the  fact  that  their  atomic  weights  vary  in  the 
same  order.  The  same  fact  has  been  noticed  in  our  study 
of  other  groups. 

NEWLAXD'S  DISCOVERY.  —  Such  facts  led  Mr.  Newland 
in  1863  to  arrange  many  of  the  elements  in  the  order  of 
their  atomic  weights,  beginning  with  the  one  whose  atomic 
weight  is  least,  and  then,  on  looking  over  the  list,  he  dis- 
covered that  the  elements  with,  like  properties  were  scat- 
tered at  about  equal  distances  apart. 


CLASSIFICATION.  265 

Let  us  leave  out  hydrogen  and  begin  with  lithium,  whose 
atomic  weight  is  next  larger  than  that  of  hydrogen,  and 
put  the  atomic  weights  under  the  symbols  of  the  elements 
in  the  order  of  value,  and  we  have 

Li         Be          B          C         N         O          F         Na 

7  9  11          12         14         16         19          23 

But  sodium,  Na,  is  like  lithium,  Li.  Both  are  metals  of 
the  alkalies,  and  univalent.  Now  begin  with  sodium  and 
go  on: 

Na         Mg         Al         Si         P         S  Cl  K 

23          24  27         28        31        32        35.5          39 

But  potassium,  K,  is  like  sodium  and  lithium,  alkaline 
and  univalent.  These  properties  are  found  in  every 
seventh  metal  in  the  list  so  far,  and  not  in  any  between. 

Let  us  write  the  list,  of  the  first  twenty-one,  in  lines 
of  seven.  Thus: 

Li  =   7   Be=   9  B  =11   C  =  12    N=14    O  =  16    F    =19 
Na  =  23   Mg  =  24  Al  =  27   Si  =  28    P  =  3l    S  =32    Cl   =35.5 
K  =39   Ca=40  Sc=44  Ti  =  48   V  =  51    Cr  =  52    Mn  =  55 

And  we  find  that  the  elements  which  are  most  alike  fall 
together,  under  one  another,  as  lithium,  sodium,  and  potas- 
sium in  the  first  column,  and  fluorine  and  chlorine  in  the 
last. 

It  is  a  curious  fact  that  if  we  add  16  to  the  atomic 
weight  of  lithium,  we  get  that  of  sodium,  with  the  same 
properties.  Add  16  again,  and  we  get  the  atomic  weight 
of  potassium,  another  element  with  the  same  properties. 
Add  about  16  to  the  atomic  weight  of  any  one  arid  we  get 
the  atomic  weight  of  another  which  has  similar  proper- 
ties. This  is  true  until  we  reach  phosphorus,  when  we 
must  begin  to  add  20  instead  of  16. 


266  CLA  SSI  PICA  TION. 

MENDELEJEFF'S  TABLE.  —  Now  the  Russian  chemist, 
Mendelejeff,  went  so  far  as  to  make  a  table  of  all  the 
known  elements  in  the  order  of  their  atomic  weights, 
and  he  found  that  all  those  elements,  which  are  most 
alike,  then  fell  into  the  same  column.  The  horizontal 
lines  of  elements  in  this  table  are  called  "series"  and 
the  columns  are  called  "  yroups."  In  all  there  are  12 
series  and  8  groups.  Three  of  these  series  are  given  on 
p.  265,  and  in  them  are  the  tirst  three  members  of  seven 
groups.  The  fact  is  that  — 

If  all  the  elements  are  placed  in  the  order  of  their  atomic 
weights  those  which  are  most  alike  will  be  found  at  regular 
distances  apart.  As  the  atomic  weights  increase,  the  same 
properties  appear,  again  and  again,  at  regular  intervals. 
This  is  known  as  the  periodic  law. 

The  Spiral  of  Elements.  —  The  table  of  elements  has 
been  made  in  many  shapes.  The  spiral  form,1  Fig.  68, 
shows  the  main  point  very  clearly,  which  is,  that  the 
elements  fall  naturally  into  groups  as  their  atomic  weights 
vary  by  regular  additions. 

We  begin  with  lithium  at  the  center,  and  wind  our  way 
around  the  spiral,  to  the  left,  until  we  come  out  at  the 
cirpumference.  Along  the  way  we  pass  by  elements  with 
larger  and  larger  atomic  weights  in  regular  order.  The 
spiral  is  divided  into  eight  sections  by  lines  from  the 
center,  and  the  elements  which  are  alike  in  properties 
are  found  together  in  these  sections.  In  fact,  this  con- 
tinuous spiral  of  atomic  weights  throws  all  the  elements 
into  eight  natural  groups. 

Take,  for  example,  our  chlorine  group,  p.  147,  whose  mem- 
bers have  been  found  to  be  so  much  alike.  We  find  them 

1  First  given  by  Baumhauer  in  1870,  then  modified  by  Huth  in 
1884,  and  adopted  by  Carnelly  in  1885.  —  Chemical  News,  Vol.  63, 
p.  184. 


CLASSIFICATION. 


267 


all  in  the  seventh  group  of  the  spiral,  brought  there  by  the 
order  of  their  atomic  weights.  We  find  all  the  members  of 
the  oxygen  group  in  the  sixth,  all  of  the  nitrogen  group 
in  the  fifth,  and  all  of  the  calcium  group  in  the  second. 


Fig.  68. 


But  in  each  of  these  "natural  groups"  in  the  spiral 
we  find  some  elements  which  have  not  before  been  put 
together.  In  the  first,  for  example,  we  find  all  the  metals 
of  the  potassium  class,  and  with  them,  copper  and  silver. 
Now  many  of  the  leading  properties  of  copper  and  silver 
are  not  like  those  of  sodium  and  potassium.  They  do  not 


268  CLASSIFICA  TION. 

agree  with  these  in  being  soft,  light,  and  combustible  on 
water.  Yet  in  some  things  they  do  agree  quite  closely. 
For  example: 

Potassium  forms  the  oxide  K2O 
Copper  "  "      Cu2O 

Silver  "  "       Ag2O 

In  these  compounds  the  atoms  of  potassium,  copper,  and 
silver  hold  the  same  relation  to  oxygen.  And  the  order 
of  their  atomic  weights  brings  them  together  in  the  same 
group  in  the  spiral. 

THE  VACANT  PLACES.  —  There  are  many  vacant  places 
in  the  spiral :  what  is  the  meaning  of  these  gaps  ?  They 
lead  us  to  think  that  the  elements  are  not  yet  all 
discovered. 

When  the  table  was  first  made  there  was  a  vacant  place 
where  gallium,  Ga,  now  stands  in  the  third  group.  Men- 
delejeff  said  that  there  ought  to  be  an  element  whose 
"atomic  weight  is  about  69,  its  specific  gravity  about  6, 
and  its  atomic  volume  about  11.5,"  to  fill  this  gap.  After- 
ward gallium  was  discovered.  Its  atomic  weight  proved  to 
be  69.8,  its  specific  gravity  5.9,  and  its  atomic  volume  11.8. 
From  its  vacant  place  in  the  table,  Mendelejeff  was  able 
to  give  the  properties  of  this  metal  before  it  had  been 
discovered.  He  did  the  same  thing  for  the  element  scan- 
dium, Sc,  also  in  the  third  group.  Possibly  other  elements 
are  yet  to  be  discovered  by  which  other  gaps  will  be 
filled. 

THE    ANALYTICAL    SYSTEM. 

Classification  Founded  on  Solubility.  —  We  have 
found  that  hydrochloric  acid  will  give  a  precipitate  if 
mixed  with  a  solution  of  a  compound  of  silver,  Ex.  193, 
but  none  if  mixed  with  a  solution  of  a  compound  of  copper, 
Ex.  185.  This  is  because  silver  chloride  is  insoluble  in 
the  liquid  used,  while  copper  chloride  is  soluble. 


CLASSIFICA  TION. 


269 


Now  all  metals  whose  chlorides  are  insoluble,  like  that 
of  silver,  can  be  put  with  silver  to  form  one  group.  Such 
differences  in  solubility  throw  the  metals  together  into 
classes  called  the  analytical  groups. 

But  we  have  found,  by  experiment,  what  many  of  the 
insoluble  compounds  of  the  metals  are,  and  we  can  see, 
from  our  experiments,  which  are  alike  and  which  not 
alike.  Indeed,  if  we  will  just  gather  up  the  facts  which  are 
scattered  among  our  experiments,  we  shall  find  the  metals 
falling  into  the  analytical  groups.  If  the  student  has 
made  the  experiments  he  will  find  it  an  interesting  and 
profitable  exercise  to  deduce  this  classification  from  them. 

To  do  this  make  a  t^ble,  with  six  columns,  like  the 
blank  form  below,  and  then  fill  the  blank  spaces  opposite 
the  numbers  in  each  column,  by  consulting  the  record  of 
the  results  obtained  by  the  experiments  with  the  metals, 
thus : 


CHLORIDES 

insoluble  in 
acid  water. 

SULPHIDES 

insoluble  in 
acid  water. 

HYDROXIDES 

insoluble  in 
NH4HO, 
andNH4Cl. 

SULPHIDES 

insoluble  in 
NH4HO. 

CARBONATES 

insoluble  in 
N  H4  H  O, 
and  N  H4  Cl. 

ALL  SALTS 

soluble. 

\ 

\ 

\ 

1  

1  

1  

2 

o 

2 

9 

9 

9 

3  

3  

3  

3  

3  

3  

4 

4  

4  

5  

6  

7  

Group  I. 
precipitated 
by  H  Cl. 

Group  II. 
precipitated 
byH2S. 

Group  III. 
precipitated 
by  NH4HO. 

Group  IV. 
precipitated 

by(NH4)2S. 

Group  V. 
precipitated 

by     (NH4)2 
C  O3  . 

Group  VI. 
not  precipi- 
tated. 

Place  in  the  first  column  a  list  of  all  the  metals  which 
will  give  a  precipitate  with  hydrochloric  acid:  you  find 
their  names  by  looking  back  over  the  experiments  under 


270  CLA  SSIFICA  TION. 

each  metal.  This  list  will  contain  the  metals  whose 
chlorides  are  insoluble  in  acid  water.  These  metals  make 
up  Group  I. 

Place  in  the  second  column  a  list  of  all  the  other  metals 
whose  sulphides  are  insoluble  in  acid  water.  These  will 
make  Group  II. 

Place  in  the  third,  a  list  of  all  metals  not  found  in 
the  first  and  second  columns  whose  hydroxides  are  not 
soluble  in  N  H4  H  0,  or  N  H4  Cl.  In  this  way  we  make 
out  Group  III. 

Place  in  the  fourth,  a  list  of  all  the  metals  not  found 
in  the  first  three  columns,  whose  sulphides  are  insoluble 
in  N  H4  H  0.  These  are  the  metals  of  Group  IV. 

Place  in  the  fifth,  all  the  remaining  metals  whose 
carbonates  are  insoluble  in  N  H4  H  0,  or  N  H4  Cl.  These 
are  the  metals  in  Group  V. 

Place  in  the  sixth,  all  the  remaining  metals  whose 
chlorides,  sulphides,  hydroxides,  and  carbonates  are  all 
soluble.  These  are  the  metals  in  Group  VI. 

We  now  find  that  our  study  of  the  metals,  by  experi- 
ment, has  not  only  given  us  the  facts  about  them  and 
their  compounds,  but  that  it  has  also  given  us  a  way  to 
detect  their  presence  in  substances  whose  composition  is 
unknown  to  us.  In  fact,  we  are  now  prepared  to  analyze 
a  salt,  thus  :  — 

To  find  out  what  Metal  a  Salt  contains.  —  If  the 
salt  is  in  the  solid  form  we  begin  by  making  a  solution 
of  it.  Then,  — 

1.  —  Taking  a  small  quantity  of  the  solution  in  a 
tube,  we  add  hydrochloric  acid  drop  by  drop.  If  a  pre- 
cipitate is  made  in  this  way,  it  shows  that  the  metal  of 
the  salt  is  one  or  another  of  the  three  in  Group  I.  And 
then,  to  learn  which  one  of  these  it  is,  we  may  try,  with 
the  solution,  the  experiments  which  are  given  under  the 


CLASSIFICATION.  271 

head  of  each  of  these  particular  metals,  in  our  previous 
study  of  them. 

But  if  the  hydrochloric  acid  yields  no  precipitate,  we 
may  say  that  the  salt  is  not  a  compound  of  any  one  of 
these  three  metals,  and  may  seek  further,  to  find  whether 
it  is  one  of  the  seven  metals  of  Group  II. 

2.  —  The  question  is,  whether  its  sulphide  is  insoluble 
in  acid  water.     And  to  answer  it,  we  take  a  little  of  the 
solution,  make  it  acid  by  adding  a  drop  or  two  of  hydro- 
chloric acid,  and  then  add   hydrogen  sulphide,  H2S.      If 
a  precipitate   is   made   in   this   way,   our   salt   is   a  com- 
pound of  one  of  the  seven  metals  of  Group  II.,  but  if 
none,   it  is  not. 

Now  the  sulphides  of  three  of  these  seven  metals  can 
be  dissolved  by  ammonium  sulphide  (N  H4)2  S,  while  those 
of  the  other  four  cannot.  So  we  may  take  a  little  of 
our  precipitate,  and  warm  it  with  ammonium  sulphide, 
and,  if  it  proves  to  be  soluble,  we  may  say  that  the  metal 
in  our  salt  is  one  of  these  three,  but  if  insoluble,  we  say 
that  it  is  one  of  the  other  four. 

In  either  case  we  may  find  out  which  particular  one 
of  the  metals  is  present,  by  making  the  experiments  given 
in  this  book  in  the  description  of  each  of  them. 

But  if  hydrogen  sulphide  has  given  no  precipitate,  we 
say  that  our  salt  is  not  a  compound  of  any  one  of  these 
seven  metals,  and  go  on  to  learn  whether  it  is  of  one  of 
the  three  in  Group  III. 

3.  —  The   question    now   is,   whether    its    hydroxide   is 
insoluble   in   ammonia  and   ammonium  chloride.     And  to 
answer  this,  we  take  a  little  of  our  first  solution,  put  into 
it,  first  a  considerable   quantity   of    ammonium   chloride, 
N  H4  Cl,  and  then  add  ammonia,  N  H4  H  0,  until  the  liquid 
smells  strongly  of  this  substance.     It  must  be  well  shaken 
and  the  air  blown  out  of  the  tube,  then  the  odor  of  ammo- 


272  CLASSIFICATION. 

ma  will  show  when  enough  has  been  added.  If  a  precipi- 
tate is  made  in  this  way,  we  may  say  that  our  salt  is  a 
compound  of  one  of  the  three  metals  in  Group  III.  And 
then,  to  know  which  one,  we  note  the  color  of  our  precipi- 
tate and  also  make  the  experiments  already  described  in 
the  study  of  these  three  metals. 

But  if  we  get  no  precipitate,  we  say  that  our  salt  cannot 
be  a  compound  of  any  one  of  these  metals. 

4. —  The  next  question  is,  whether  the  sulphide  of  the 
metal  we  are  after  is  insoluble  in  ammonia  water.  And 
to  answer  this,  we  take  a  little  of  our  first  solution,  and  put 
a  little  ammonia  with  it,  then  add  ammonium  sulphide 
drop  by  drop.  A  precipitate  now  shows  that  our  salt  is 
a  compound  of  one  of  the  four  metals  in  Group  IV.  We 
then  decide  which  one  of  the  four,  by  noting  the  color  of 
the  sulphide,  and  also  making  the  experiments  given  in 
our  description  of  these  metals. 

No  precipitate  here,  with  ammonium  sulphide,  proves 
that  no  one  of  these  four  metals  is  present  in  our  salt. 

5. — We  next  ask,  whether  the  carbonate  of  our  metal 
is  insoluble  in  ammonia  and  ammonium  chloride,  for  if 
it  is,  then  our  metal  is  one  of  the  four  in  Group  V. 

To  a  little  of  the  solution  of  our  salt  we  add  consid- 
erable ammonium  chloride,  N  H4  Cl,  and  then  add  ammo- 
nium carbonate  (NH4)2CO3.  If  we  get  a  precipitate,  we 
next  decide  which  one  of  the  four  metals  of  Group  V.  is 
present  in  our  salt,  by  the  experiments  already  given  in 
the  study  of  these  metals. 

But  if  no  precipitate  is  made,  these  four  metals  are 
thrown  out  of  the  question,  and  our  salt  must  then  be  a 
compound  of  one  of  the  metals  in  Group  VI. 

6.  —  Which  one  of  these  four  is  it  ?  This  is  the  final 
question.  To  answer  it,  we  may  make  the  experiments 
which  are  given  in  the  descriptions  of  these  metals,  and 
see  with  which  of  the  four  our  results  agree. 


CLASSIFICA  TION.  273 

By  following  the  order  of  the  groups  in  this  regular 
way,  one  can  bring  out  the  metal  of  almost  any  simple 
salt,  with  certainty  and  very  quickly. 

The  student  may  do  this  with  a  few  simple  salts  whose 
names  he  does  not  know.  The  teacher  will  select  them 
and  keep  a  record  of  their  names,  and  at  the  end  of 
his  work  the  student  should  report  his  work  and  the 
result  of  it.  He  should  write  down,  in  a  short  way, 
every  experiment  he  makes,  and  what  the  result  of  it 
is,  and  what  it  proves;  and  he  should  do  this  for  each 
experiment,  at  the  time  he  makes  it,  and  not  wait  until 
others  are  made. 

On  page  275  is  a  copy  of  one  report  of  an  "analysis," 
which  shows  a  form  of  the  notes  to  be  kept  in  each  case. 
Notice  that,  below  the  heading,  which  is  the  name  of 
the  student,  date  of  the  work,  and  number  of  the  sub- 
stance, the  sheet  is  divided  into  three  columns.  In  one, 
is  put  a  brief  description  of  all  the  experiments  made. 
In  the  second,  the  result  of  each  is  written,  and  in  the 
third,  the  fact  which  it  proves. 

To  find  out  what  Acid  the  Salt  contains.  —  But 
when  we  have  found  the  metal  in  a  salt,  we  do  not 
yet  know  the  name  of  the  salt.  It  may  be  a  nitrate,  a 
chloride,  or  some  other  compound.  The  next  step  is  to 
identify  the  acid  part  of  it.  This  is  done  by  making 
the  tests  which  were  described  in  our  study  of  the  non- 
metals,  or  the  experiments  described  in  the  Exercises. 
Thus  a  test  for  sulphuric  acid  is  given  on  p.  167,  and 
the  use  of  it,  to  show  whether  a  substance  is  a  sulphate, 
is  illustrated  in  Ex.  122.  See  also  the  Exercises,  p.  173. 
Hydrochloric  acid,  or  its  salts,  —  the  chlorides,  —  may  be 
identified  by  the  test  on  p.  147.  See  also  the  exercises  on 
p.  151.  Nitric  acid,  and  the  nitrates  also,  may  be  detected 
by  the  "  Copperas  Test,"  p.  100.  If  a  salt  is  a  carbonate 


274  ( 'L.  1 SSIFICA  TION. 

it  will  effervesce ,  when  treated  with  dilute  acid,  and  the 
gas  which  is  set  free  will  whiten  lime-water. 

In  this  work  for  the  acid,  as  in  that  for  the  metal, 
brief  notes  of  all  the  experiments  should  be  made,  and  re- 
ported. 

To  Name  the  Salt.  —  Having  found  what  metal  a  salt 
contains,  and  also  what  the  acid  part  of  *it  is,  you  can  de- 
clare the  name  of  the  salt  which  was  given  you  for  analysis 
(p.  136).  For  example,  having  found  strontium  and  nitric 
acid,  the  substance  itself  must  be  strontium  nitrate. 

In  this  way,  a  "simple"  salt,  that  is,  a  salt  which 
contains  only  one  acid  and  one  metal,  may  be  analyzed. 
The  work  is  a  most  valuable  exercise  for  the  student  at 
this  stage  of  his  progress,  and,  with  a  good  reference  book 
at  hand,  it  should  be  carried  as  far  as  time  will  permit. 

Hint  as  to  further  Work. — Even  "complex"  sub- 
stances, that  is,  substances  which  contain  more  than  one 
metal  or  acid,  may  be  analyzed  by  very  natural  additions  to 
the  foregoing  work.  If,  for  example,  we  have  a  mixture 
of,  say,  silver  and  copper  nitrates,  we  can  detect  both  the 
silver  and  the  copper.  For  we  can  separate  them  by  using 
H  Cl,  as  was  done  in  Ex.  195. 

If  our  mixture  should  contain  one  metal  of  every  group, 
still  every  one  of  them  could  be  "separated,"  and  then 
"  identified,"  by  just  such  work.  In  such  a  case  we  could 
use  the  group  reagents  (see  bottom  of  table,  p.  269)  one 
after  another,  in  regular  order.  H  Cl  would  take  out  all 
of  the  metal  of  Group  I.,  and  leave  all  the  others  in  solu- 
tion. Every  group  reagent  in  its  order  would  precipitate 
all  of  the  metal  of  its  group,  and  leave  all  those  of  groups 
that  come  after  in  solution.  In  this  way  we  should  get 
each  metal  alone,  and  could  then  identify  it.  Of  course, 
if  a  group  reagent  gives  no  precipitate,  all  metals  of  its 
group  must  be  absent. 


CLASSIFICA  TION. 
REPORT   OF   AN   ANALYSIS. 

Name Date. 

Substance  No._. 


275 


EXPERIMENTS. 

RESULTS. 

INFERENCES. 

I.   Add  drops  of  HC1. 

No  precipitate  made 

Absence  of  Group  I. 
Ag,  Hg  (ous),  and 
Pb. 

II.   To  I.  addH2S. 

No  precipitate  made 

Absence  of  Group  II. 
Hg(ic),  Bi,Cu,Cd, 
As,  Sb,  Sn. 

III.  To  the  original 
solution  add  NH4C1 
and  N  H4  H  O. 

No  precipitate  made 

Absence  of  Group 
III.  Fe,  Al,  Cr, 

IV.   To    III.     add 
(NH4)2S. 

No  precipitate  made 

Absence  of  Group 
IV.  Mn,  Zn,  Ni, 
Co. 

V.    To  original  solu- 
tion   add    NH4C1 
and(NH4)2C03. 

A  white  precipitate 

Presence  of  Group  V. 
Ba,  Sr,  or  Ca. 

VI.   To  the   original 
solution  add    solu- 

No precipitate  made 
in  the  cold 

Absence  of  Ba. 

tion  of  Ca  S  04  . 

VII.  Heat  VI.  to  boil- 

A white  precipitate 

Presence  of  Sr. 

ing. 

Vllt.   Flame-test. 

Brilliant  crimson 

Confirms  presence 
of  Sr. 

Hence  substance  No is  a  compound  of  strontium. 


APPENDIX. 


THE     APPARATUS. 

THE  following  list  contains  the  pieces  in  a  single  set  of  ap- 
paratus for  the  course  of  experiments  described  in  this  book. 
The  full  set  is  shown  in  the  cut,  Fig.  69.  It  is  designed  for 
the  use  of  beginners,  unused  to  manipulation,  and  of  teachers 
who  are  oftentimes  so  pressed  by  other  duties  that  little  time 
remains  for  the  preparation  of  experiments.  Selected  from  the 
standard  articles  in  the  outfit  of  the  chemist,  they  are  neat 
in  appearance,  efficient  in  action,  easily  put  together,  and 
comparatively  cheap.  The  forms  shown  in  the  cut  are  of  the 
pieces  which  have  been  actually  used  in  devising  and  testing 
the  experiments  described. 

Fragile  articles,  such  as  test-'aibe3  rj.d  flasks,  should  be 
bought  in  quantity,  to  allow  for  breakage.  One  balance  will 
serve  several  workers.  The  same  is  true  of  the  thermometer, 
where  economy  must  be  practiced,  and  a  single  graduated 
cylinder  for  each  will  do  very  well,  although  in  that  case  all 
cannot,  at  one  time,  make  Ex.  37. 

The  pieces  are  here  described  in  the  order  of  their  numbers 
in  the  cut. 

1.  Graduated     Cylinder.  —  A   tall    and    narrow    glass 
cylinder  on  foot,  about  $  inches  in  diameter,  25  cc.  graduated 
to  halves. 

Number  required  in  single  set 2 

2.  Test-tubes  and  Rack. — Tubes  6  inches  long  by  f 
inch  in  diameter.    They  should  be  bought  by  the  gross.     The 
rack  to  support  the  tubes  can  be  made  by  any  carpenter.     Its 
form  is  shown  in  the  cuts. 

Number  required  in  single  set 12 

279 


280  APPENDIX. 

3.  Side-neck  tube.  — Of  German   or  soft  glass,  and  of 
Bohemian  or  hard  glass,  6  x  £  inches.     They   may  be  bought 
by  the  dozen,  and  kept  in  stock. 

Number  required  in  single  set,  of  soft  glass    .     .      1 

"    hard    "...      1 

4.  Mortar  and  Pestle.  —  Of  glass  or  porcelain,  glazed 
inside  and  outside,  3£  inches  diameter. 

5.  Support  with  Ring  and  Clamp.  —  The  support   is 
of  iron.     It  is  the  so-called  retort-stand.     We  select  the  small 
size,  usually  provided  with  two  rings.     Only  one  ring  is  called 
for,  but  the  second  will  be  found  useful.     These  rings  should 
be  arranged,  as  shown,  to  be  taken  off  at  the  side  of  the  rod. 
The  clamp  is  "small  size  "  with  "  universal  movement,"  to  hold 
a  tube  or  flask  in  horizontal  or  vertical  or  oblique  position. 

6.  Side-neck  Flask.  —  A  round  bottom  flask  with  a  side 
neck  attached  to  the  stem. 

Number  required  for  each  student's  set,  150  cc.     .      1 

"      the  teacher's  set,  150  cc.     .      1 

and  250  cc.     .      1 

7.  Conical  Flasks. — The  so-called    Erlenmeyer  flasks, 
or  Beaker  flasks.     These  are  thin  and  rather  fragile,  but  with 
care  will  last  a  long  time.     Their  freedom  from  color,  perfect 
transparency,   uniformity    in    shape    and    size,    render    them 
peculiarly  well  fitted  for  the  examination  of  gases  and  liquids. 
Flasks  of  the  usual  form,  or  bottles,  may  be  used  instead  of 
these,  and,  if  made  of  white  glass,  and  have  mouths  of  uniform 
size,  to  be  perfectly  closed  by  the  stoppers,  bottles  are  very  good 
and  more  durable.     The  mouth  should  be  f  to  1  inch  in  diam- 
eter, taking  a  No.  4  or  No.  5  E.  &  A.  soft  rubber  stopper. 

The  use  of  these  flasks  and  bottles,  as  described,  for  collect- 
ing and  examining  gases,  dispenses  with  the  pneumatic  cistern, 
and  the  unpleasant  wetness  which  goes  with  it.  This  method 
also  enables  one  to  dispose  of  noxious  substances  with  gratify- 
ing success. 

For  each  student  200  cc.  or  6  oz.  flasks 4 

For  the  teacher,  200  cc.  or  6  oz.  flasks 2 

500  cc.  or  16  oz.  flasks          ...      4 


UII71RSIT7 


8,9.  Rubber  stoppers.  —  Success  in  managing  gases 
by  this  method  demands  that  all  joints  in  the  apparatus  shall 
be  air-tight.  Such  joints  are  easily  made  by  means  of  rubber 
stoppers  No.  9,  arranged  with  glass  tubes  No.  8.  Each  flask  or 
bottle  is  to  be  supplied  with  this  arrangement,  and  they  are  then 
to  be  joined  together  by  rubber  tubing.  The  first  cost  of  rubber 
stoppers  is  larger  than  of  cork,  but  their  durability  is  a  compen- 
sation. They  should  be  of  the  "best  soft  rubber,"  and  of  such 
sizes  as  to  fit  the  mouths  of  the  flasks  and  tubes  in  use.  Their 
sizes  are  described  by  numbers,  but  the  same  number,  used 
by  different  makers,  does  not  always  describe  the  same  size  or 
quality.  To  be  definite,  we  now  refer  to  those  stamped  "  E. 
&  A."  (Eimer  and  Amend). 

No.  3  will  fit  a  f-  inch  tube  or  flask  or  bottle. 
No.  4     "      "       J    "      flask  or  bottle. 
No.  5     "      "       1    "          "  bottle. 

One  "  solid  "  will  be  needed,  to  close  the  side-neck  tube  or 
flask  ;  one  "  with  two  holes,"  to  close  each  flask  or  bottle  in 
use. 

1C.  Bunsen  Burner.  —  In  laboratories  not  supplied 
with  gas,  the  alcohol  lamp  is  the  best  substitute. 

11.  Glass  Funnel.  —  The  best  German  make,  with  long 
thin  stem.     Diameter  2£  inches. 

12.  Wide-mouth  Bottles.  —  Flint  glass,  tall  style. 

Bottles  should  be  bought  by  the  dozen,  or  in  larger  labora- 
tories by  the  gross. 

Needed  for  each  set,  wide-mouth,  200  cc.  or  8  oz.  .      1 

extra  wide-mouth,  200  cc.  "      "     .      1 

wide-mouth,  400  cc.  "  16  oz.       1 

13.  Forceps.  —  Steel,  plain,  4£  inches. 

14.  Glass  tubing.  —  Made   of   the  best  German   or  soft 
glass.     It  should  be  of  such  size  as  to  fit  the  holes  in  the  rubber 
stoppers  used,  about  &  inch  outside  diameter  for  those  de- 
scribed above.    It  may  be  cut  into  pieces,  of  any  length  desired, 
by  first  drawing  across  it  the  edge  of  a  sharp  three-cornered 


282  APPENDIX. 

file,  once,  making  a  distinct  scratch,  and  then  pulling  the  tube, 
almost  but  not  quite  lengthwise.      The  sharp  cut  edges  may 
be  rounded  by  heating  them  until  red  in  the  lamp-flame. 
Glass  tubing  is  to  be  bought  by  the  pound. 

15.  Porcelain     Dish.  —  So-called    "  evaporating     dish." 
The  R.  B.  porcelain  is  best.     Diameter  3£  inches. 

These  may  be  bought  by  the  dozen. 

Needed  for  each  set 1  or  2 

16.  Drying  Tube.— The  so-called  "chloride  of  calcium 
tube,"  with  one  bulb,  length  5  inches. 

17.  Pinch-cock.  —  Mohr's,  small  size,  strong. 

18.  The  Balance.  —  A  balance  of   good  quality  is  the 
most  costly  piece  in  the  outfit  for  laboratory  work.    In  quali- 
tative chemistry,  such  as  the  foregoing  course,  it  is  not  abso- 
lutely indispensable,  because  something  can  be  done  by  means 
of  cheap  substitutes,  —  even  by  such  as  an  ingenious  student 
can  make. 

The  balance  shown  in  the  cut  is  a  Becker's  balance,  listed 
in  "  Becker  Brothers"  catalogue  as  No.  14,  at  $11.00.  With  a 
glass  case,  which  is  very  desirable  to  protect  the  instrument 
from  dirt  and  corrosion,  it  is  listed  as  No.  16,  at  $  22.00.  It  is 
neat,  accurate,  sensitive  to  2  ing.,  and  durable. 

The  weights  for  this  balance  should  be  a  set  of  50  g.  to  1  g. 
in  brass,  and  500  mg.  to  1  mg.  in  platinum  or  aluminum 
with  forceps,  all  in  a  lined  and  covered  box.  Such  a  set  is 
listed  by  Becker  Brothers  at  $9.00,  and  by  Eimer  and  Amend 
at  $5.50. 

From  parties  (John  Wanamaker,  Philadelphia)  who  import 
from  Becker's  Sons  of  Rotterdam,  the  balance  and  weights 
just  described,  or  their  equivalent,  can  be  obtained  by  schools, 
free  of  duty,  at  much  less  cost. 

19.  The  Water  Pan.  —  A  pan  about  8  inches  diameter, 
and  3  or  4  inches  deep,  with  flat  bottom  and  straight  walls. 
It  may  be  of  glass  —  a  so-called  crystallizing  dish,  as  shown  in 
the  cut,  or  it  may  be  of  agate-iron  ware,  which  is  likely  to  be 
more  durable,  but  less  shapely. 


APPENDIX.  283 

20.  A  common  Plate. —  A  small  size  china  plate. 

21.  Rubber  Tubing.  — To  connect  the  Bunsen  Burner 
with  the  gas  supply,  white  rubber,  thick,  £  inch  diameter  inside, 
may  be  used.     Red  rubber  is  better,  and  a  little  more  costly. 

For  joining  parts  of  the  gas-apparatus  the  black  or  red 
tubing,  of  usual  thickness,  is  to  be  preferred.  The  size  should 
correspond  with  that  of  the  glass  tubing,  which  it  must  fit. 
Rubber  tubing  is  bought  by  the  foot.  In  pieces  of  12  feet  it 
comes  a  little  cheaper. 

22.  A  Chemical  Thermometer.  —  A  Centigrade  ther- 
mometer, graduated  from  about — 20°  to  +200°.     The  best  in- 
strument has  its  scale  on  the  glass  stem  itself.     A  cheaper  and 
very  good  instrument  has  a  paper  scale   enclosed  in  a  glass 
tube,  which  protects  the  stem. 


THE    CHEMICALS. 

IN  the  following  list  may  be  found  the  names  and  formulas 
of  all  the  substances  required  to  make  the  experiments  de- 
scribed in  this  book.  Chemicals,  to  be  used  in  the  study  of 
chemistry,  should  be  of  the  best  quality.  Many  of  those  fur- 
nished by  the  shops  are  impure,  and  often  lead  to  wrong  and 
troublesome  results.  It  is  better  to  buy  chemicals,  as  you  buy 
apparatus,  from  well-known  dealers  in  laboratory  supplies. 

Reagents,  which  are  to  be  used  by  students,  should  be  kept 
upon  their  tables  in  small  bottles :  liquids  in  glass-stoppered 
bottles  holding  about  125  cc.  or  four  oz.,  and  solids  in  salt-mouth 
bottles  holding  2  oz.  If  substances  are  to  be  used  by  the 
teacher  they  may,  for  the  most  part,  be  kept  in  the  bottles  in 
which  they  are  bought.  Every  bottle  should  be  distinctly  and 
permanently  labelled. 

Unless  economy  must  be  rigidly  practiced,  the  supply  will  not 
be  limited  to  the  substances  in  this  list;  specimens,  in  great 
variety,  are  very  desirable. 

The  author  will  gladly  give  any  information  he  can  in  regard 
to  the  purchase  or  use  of  apparatus  and  chemicals. 

Acetic  acid,  pure        ....        .    HC2H3O2 

Alcohol  .        .        .        ,  .        C2H60 

Alum       .  .....     K2A12(S04)4  +  24H20 

Ammonium  carbonate,  C.  P.  .        (N  H4)2  C  O3 
chloride,  C.  P.       .        .    NH4C1 

hydrate     .        .  .         NH4HO 
nitrate,  cryst.        .        .     NH4NO3 

Antimony  chloride,  sol.  C.  P.  .         Sb  C18 

Arsenous  oxide  .        •'       .        •        -    Asa  O, 

Barium  chloride,  C.  P.   .        .  *•.      Bad, 

284 


APPENDIX.  285 

Bismuth  nitrate,  cryst.  C.  P.  .  Bi  (N  03)3 

Bone-black C 

Bromine Br 

Calcium  chloride,  crude         .        .  Ca  C12 

cryst.  C.  P.     . 

"        oxide  (quicklime)  .        .  Ca  O 

Carbon  pencil C 

Chrome  alum          ....  K2  Cr2  (S  04)  4  +  24  H2  0 

Cobalt  nitrate,  C.  P.    .        ....  Co(N03)2 

Cochineal        .        .  ,      ;'.i     .    •    . 

Copper,  thin  sheet     .        .        .        .  Cu 

chloride    .        .        .      . .  Cu  C12 

sulphate,  C.  P.      .        .        .  Cu  S  04 

Dutch  metal  (imitation  gold-leaf)  Cu  Zn 

Ferrous  sulphate,  pure       .        .        .  Fe  S  O4 

"       sulphide  (sticks)       .        .  Fe  S 

Hydrochloric  acid,  pure  .        .  H  Cl 

Iodine I 

Lead  acetate       .        .       '.   -     .        .  Pb  (C2  H3  O2)2 
Litmus  (blocks)      .        .        . 
Logwood     .    '    .        .        .        .        *-' 

Magnesium  (ribbon)      .        .        .  Mg 

chloride,  cryst.       .        .  Mg  C12 

sulphate,  C.  P.   .        .  Mg  S  O4 

Manganese  dioxide,  powder      .        .  Mn  02 

sulphate       .        .    -    .  MnSO4 

Marble CaC03 

Mercury,  redistilled        .        .        .  Hg 

Mercuric  chloride  (cor.  sub.)     .        .  Hg  C12 

oxide       .        .        .        .  HgO 

Nickel  chloride M  C12 

Nitric  acid,  pure     .        «        »   ,     ,   -  H  N  08 

Oxalic  acid,  C.  P H2  C2  O4 

Paraffine         .        .        ,        .        .  Cn  H2n    2 

Phosphorus P 

Potassium K 

bromide,  C.  P.    .        .        .  K  Br 

"         carbonate,  C.  P.     .        .  K2  C  Os 


286  APPENDIX. 

Potassium  chlorate,  cryst.          .        .  K  Cl  O3 

chroma  te       ...  K2  Or  O4 

dichromate        .        .        .  K2Cr2O7 

ferrocyanide          .        .  K4  Fe  Cy6 

"         hydrate,  pure    .        .        .  K  H  O 

iodide,  C.  P.  .        ....  K I 

nitrate,  cryst.     .        .        .  K  N  O8 

"         sulphate,  cryst.      .         .  K2SO4 

Platinum  foil Pt 

"        wire        ....  Pt 

Pyrogallic  acid   .  .        .  C6  H3  (H  O)3 

Silver  nitrate,  cryst.        .        .        *    .  AgN03 

Sodium        .      ^.^4.'    —.        .        .  Na 

biborate  (borax)        .      ;^  /  Na2  B4  O7  +  10  II2  O 

carbonate,  C.  P.     .        .  .     .  Na2  C  O3 

hydrate,  C.  P.    .        .   ...  .  Na  H  O 

"       nitrate    .        .      ;.   .     .        .  NaNO3 

"       sulphate     ....  Nn,SO4 

Strontium  chloride     .        .        .        .  Sr  C12 

nitrate,  C.  P.          .        .  Sr  (N  03)2 

Sulphur,  flowers  .  S 

roll  .        .       .,v     ...  S 

Sulphuric  acid,  pure  .        .    .    .        .  H2  S  O4 

Tartaric  acid,  cryst.        .  C4IF608 

Tin  (granulated)     .  *  •.;.-.        .        .  Sn 

Zinc  (sheet)    .        .        .     -  .     -  * .  ,  Zn 

"       (granulated)     .        .        .        .  Zn 

Sugar  (granulated)        >. !  -'     .        .    ,  C12  H22  O^ 

Salt      .        .        *     Jv^;t-    .    •        •  NaCl 

Charcoal         .        .        .        .        .    .  C 

METRIC  AND  ENGLISH  MEASURES. 

Measures   of  Weight. 

10  milligrams,  mg.  =  1  centigram,  eg.  =  0.154  grains. 
10  centigrams,  eg.  =  1  decigram,  dg.  =  1.543  grains. 
10  decigrams,  dg.  =  1  GRAM,  g.  =  15.432  grains. 

10  grams  =  1  decagram         =  154.323  grains. 

10  decagrams          =  1  hectogram        =      3.527  oz.  avoir. 
10  hectograms         =  1  kilogram  =     2.204  Ib.  avoir. 


APPENDIX.  287 

1  grain       =    0.0648  g.  or  04.799  mg. 

1  oz.  Troy  =  31.1035  g.  1  oz.  avoir.  =  28.349  g. 

1  Ib.  Troy  =  5760  grains.  1  Ib.  avoir.  =  7000  grains. 

Measures  of  Volume. 

10  cubic  centimeters,  cc.  =  1  centiliter,  cl     =     0.338  fld.  oz. 
10  centiliters  =  1  deciliter  =      0.845  gill. 

10  deciliters  =  1  LITER,  1.  =      1.057  quart. 

10  liters  =  1  decaliter  =      2.642  gal. 

10  decaliters  =  1  hectoliters,  hi.  =    26.417  gal. 

10  hectoliters  =  1  kiloliter  =  264.18  gal. 

1  cu.  in.       =  16.386  cc.  1U,  S.  quart  =     0.9469  1. 

1  liter          =  61.027  cu.  in.  1  U.  S.  gal.     =      3.785  1. 

1  U.  S.  gal.  =  231  cu.  in.  1  Imp.  gal.     =  277.25  cu.  in. 

Measures  of  Length. 

10  millimeters,  mm.  —  1  centimeter,  cm.  —     0.3937  in. 
10  centimeters  =  1  decimeter  —      3.937    in. 

10  decimeters  —  1  METER,  m.  =    39.37  in. 

10  meters  =  1  decameter          =    32.8  ft. 

10  decameters  =  1  hectometer         =  328.08  ft. 

10  hectometers          =  1  kilometer,  km.    =     0.62137  mile. 

1  inch  =  2.534  cm.  1  millimeter  -  0.0393  in. 

1  yard  =  0.9144  m.  1  meter         =  1.0936  yd. 

1  mile  =  1.6093  km.  1  kilometer  =  about  f  mile. 

Measures  of  Temperature. 

Freezing-point  of  water  =      0°  Centigrade,  C.  or   32°  Fahrenheit,  F. 
Boiling-point  of  water    =  100°         "  or  212°         " 

1°  C.  =  f°,  or  1.8°  F.  1°  F.  =  f°,  or  0.555°  C. 

To  change  a  Centigrade  temperature  to  its  equivalent  Fahren- 
heit temperature :  Multiply  by  f  and  add  32°  to  the  product. 

To  change  a  Fahrenheit  temperature  to  its  equivalent  Centi- 
grade temperature:  Subtract  32  and  multiply  the  remainder 
by  f. 


INDEX. 


THE   NUMBERS   REFER    TO   PAGES. 


ABSORPTION,  analysis  by,  70,  82. 

of  gases  by  charcoal,  106. 

of  gases  by  water,  59,  86,  146. 

of  hydrogen  by  palladium,  261. 
Acid-forming  elements,  192,  236. 
Acids,  129. 

action  of,  on  bases,  133. 

action  of,  on  metals,  134. 

chief  characteristic,  130. 

classes  of,  130. 

dibasic,  172. 

monobasic,  173. 

names  of,  135. 
Acid  salts,  173. 
Agate,  184. 
Air  spoiled  by  breathing,  79. 

analysis  of,  69-74. 

in  water,  59. 
Alkalies,  metals  of,  204. 
Allotropism,  39. 
Alloys,  214. 

of  antimony,  235. 

of  bismuth,  235. 

of  copper,  248. 

of  gold,  260. 

of  mercury,  251. 

of  osmium,  261. 

of  silver,  256. 
Alum,  233. 

ammonium,  233. 

chrome,  230. 


Alumina,  233. 
Alluminum,  233. 

compounds  of,  233. 

compounds  in  dyeing,  234. 

hydroxide,  234. 

oxide,  233. 

reactions  of,  234. 

sulphide,  234. 
Amalgams,  251. 
Amalgamated  zinc,  26. 
Amalgamation  in  metallurgy,  255, 

259. 
Amethyst,  oriental,  233. 

quartz,  183. 
Amine,  182. 
Ammonia,  84-90. 

absorbed  by  charcoal,  106. 

absorbed  by  water,  86,  88. 

composition  of,  90. 

in  food  of  plants,  102. 

in  air,  69,  85. 

Nessler's  test  for,  99. 

preparation  of,  85. 

solubility  of,  88. 

sources  of,  84,  85. 
Ammonium,  201-204. 

alum,  233. 

a  metal,  202. 

chloride,  19. 

disulphide,  203. 

hydrate,  87. 


290 


INDEX. 


Ammonium,  hydrosulphide,  203. 

reactions  of,  203. 

salts,  88,  202. 

sulphides,  160,  203. 
Analysis,  defined,  24,  50. 

by  absorption,  70,  82. 

by  electricity,  51. 

grouping  for,  269. 

notes  of  work  in,  273,  275. 

of  air,  69-74. 

of  a  metallic  salt,  270-275. 

of  a  complex  salt,  274. 

of  a  simple  salt,  274. 

of  unknown  substances,  270. 

of  water,  50-55. 

report  of  an,  275. 

systematic,  268. 
Anhydride,  defined,  165. 

arsenic,  180. 

arsenous,  179. 

carbonic,  184. 

phosphoric,  177. 

phosphorus,  177. 

silicic,  184. 

sulphuric,  169. 

sulphurous,  166. 
Animal  charcoal,  108. 
Antimonetted  hydrogen  (stibine), 

235. 
Antimony,  235. 

alloys  of,  235. 

compound  with  hydrogen,  235. 

group,  236. 

ores  of,  235. 

reactions  of,  237. 

related  to  non-metals,  235. 

sulphide,  237. 

Apparatus  for  this  course,  279. 
Aqua  regia,  92, 143,  260. 
Arsenuretted    hydrogen    (arsine), 
180. 


Arsenic,  178-182. 

acid,  180. 

Marsh's  test  for,  181. 

native,  179. 

oxides,  179,  180. 

reactions  of,  237. 

related  to  metals,  236. 

sulphide,  237. 

white,  179. 
Arsenous  oxide,  179. 
Arsenical  pyrites,  179. 
Arsenites,  180. 
Arsine,  182. 
Atmosphere,  chemistry  of,  65-83. 

a  mixture,  74. 

analysis  of,  69. 

composition  of,  73, 75. 

constituents  in,  69. 
Atomic  theory,  123. 

weights,  118,  124. 
Atomic    weights    and   properties, 

facts  from  the  Cl.  group,  151. 

facts  from  the  S.  group,  162. 

facts  from  the  N.  group,  182. 

facts  from  the  Ca.  group,  210. 

facts  from  the  Zn.  group,  216. 

facts  from  the  Fe.  group,  231. 

Newland's  discovery,  264. 

Mendelejeff 's  system,  266. 

shown  in  spiral  form,  267. 

suggests  new  elements,  268. 
Atoms,  122. 
Avogadro's  law,  122. 

BAKING  POWDERS,  200. 
Baking  soda,  40,  200. 
Barium,  210. 

reactions  of,  211. 
Base-forming  elements,  192. 
Bases,  defined,  133. 

action  on  acids,  133. 


IXDEX. 


291 


Bases,  names  of,  130. 

Basic  salts,  245. 

Battery,  voltaic,  51. 

Bell-metal,  248. 

Bessemer  process  for  steel,  226. 

Bismuth,  235. 

reactions  of,  237. 

related  to  non-metals,  236. 

sulphide,  237. 
Black-ash,  200. 
Black-lead,  110. 

Black  oxide  of  manganese,  217. 
Blast-furnace,  221. 
Bleaching,  by  chlorine,  140. 

by  sulphurous  oxide,  165,  166. 

powder,  141,  208. 
Blende  zinc,  212. 
Blistered  steel,  226. 
Bloodstone,  183. 
Boiling-point,  61. 
Bone-ash,  178. 
Borax,  185. 
Boric  acid,  186. 
Boron,  185. 

valence  of,  190. 
Brass,  214,  248. 
Brimstone,  155. 
Bromides,  148. 

reactions  of,  151. 
Bromine,  148. 
Bronze,  248. 
Bunsen  burner,  10,  47. 

CADMIUM,  215. 
Caesium,  204. 
Calamine,  212. 
Calcium,  206-211. 

carbonate,  206-208. 

chloride,  86,  207. 

flame  color  of,  211. 

group,  210. 


Calcium  hydroxide  (slaked  lime), 
207. 

hypochlorite,  208. 

insoluble  compounds  of,  208. 

occurrence,  206. 

oxide  (quick-lime),  206. 

phosphate,  178. 

reactions  of,  211. 

soluble  compounds  of,  210. 

sulphate,  208,  210. 
Calcium  carbonate,  1 13,  206. 

decomposed  by  acids,  207. 

decomposed  by  heat,  206. 

dissolved  by  water,  208. 

precipitated,  113. 
Calomel,  252. 
Calorie,  32. 
Carbon,  103-112. 

allotropic  forms  of,  111. 

compounds     with     hydrogen, 
115. 

constituent  of  plants,  101. 

diamond,  109. 

dioxide,  112. 

from  sugar,  12. 

graphite,  110. 

group,  184. 

lamp-black,  105. 

manufacture  of  charcoal,  104. 

monoxide,  115. 

source  of,  in  plants,  103. 
Carbonates,  184. 

basic,  245,  248. 
Carbon  dioxide,  112-114. 

absorbed  by  plants,  81. 

a  constituent  of  air,  74. 

by  burning  charcoal,  18. 

preparation  of,  112. 

properties  of,  113. 

product  of  combustion,  42. 

product  of  respiration,  78. 


292 


INDEX. 


Carbon,  synthesis  of,  36. 

test  for,  17,  36, 113. 
Carbon  monoxide,  82,  115. 
Carbonic  acid,  184. 

anhydride,  184. 
Carnelian,  184. 
Cast-iron,  222. 
Catalysis,  35. 
Caustic  potash,  197. 
Caustic  soda,  200. 
Cementation,  226. 
Chalcedony,  184. 
Changes,  of  two  kinds,  14. 
Charcoal,  105. 

action  of,  on  colors,  108. 

action  of,  on  gases,  106. 

action  of,  on  oxides,  109. 

a  disinfectant,  107. 

animal,  108. 

combustion  of,  36. 
Chemical  change,  13-40. 

a  change  in  molecules,  122. 

agents  to  produce,  28. 

a  source  of  electricity,  25. 

a  source  of  heat,  25. 

a  source  of  light,  27. 

combination,  17. 

decomposition,  14. 

double  decomposition,  21. 

exercises  in,  39. 

substitution,  19. 
Chemical  calculations,  127. 
Chemical  names,  135. 
Chemicals  for  this  course,  284. 
Chemistry,  how  to  study,  9,  12. 
Chilian  saltpetre,  90. 
Chlorides,  141-147. 

hydrogen-chloride,  145. 

preparation  of,  by  aqua  regia, 
92. 

preparation  of,  by  chlorine  gas, 
141. 


Chlorides,  preparation  of,  by  chlo- 
rine water,  142. 

preparation  of,  by  hydrochloric 
acid,  142. 

reactions  of,  151. 

test  for,  147. 

two,  of  one  metal,  144. 
Chlorine,  138-147. 

action  of,  on  metals,  140,  141. 

a  disinfectant,  140. 

bleaching  by,  140. 

group,  147. 

preparation  of,  138. 

properties  of,  139. 

test  for,  147. 
Chlorine  group,  147-153. 

general  behavior,  151. 

hydrogen  compounds  of,  150. 

members  of,  described,  148, 149. 

properties  and  atomic  weights 
of,  151. 

reactions  of,  151-153. 
Choke-damp,  114. 
Chrome  alum,  230. 

yellow,  230. 

Chromic  iron  (chromite),  229. 
Chromite,  229. 
Chromium,  229. 

compounds  of,  230. 

reactions  of,  230. 
Chrysoprase,  183. 
Cinnabar,  251. 
Classes,  how  made,  262. 
Classification,  262-275. 

analytical,  of  metals,  268. 

a  natural  system,  264. 

in  a  spiral  form,  266. 

Mendelejeff's  table,  266. 

metals  and  non-metals,  236, 262. 

of  metals,  262. 

of  non-metals,  261. 
Clay,  233. 


INDEX. 


293 


Clay-iron  stone,  221. 
Coal,  105. 
Cobalt,  220. 

"fly-poison,"  178. 
Coin,  analysis  of,  257. 

gold,  260. 

silver,  256. 
Combination,  17. 

by  volume,  55, 146,  147. 

law  of,  by  volume,  147. 

law  of   constant  proportions, 
57. 

law   of   multiple   proportions, 

97,  123. 

C6mbining  weights,  98. 
Combustion,  37,  41-49. 

a  mutual  action,  42. 

imperfect,  42. 

of  hydrogen  and  oxygen,  43. 

produces  heat,  43. 

produces  light,  46, 49. 

produces  compounds,  42. 
Complex  salts,  274. 
Compounds  defined,  24. 

differ  from  elements,  122. 

formulas  of,  124. 

neutral,  134. 
Constituent,  24. 
Copper,  247-251. 

alloys  of,  248. 

arsenite,  180. 

carbonate,  248. 

chloride,  141,  250. 

compounds  of,  248. 

extraction  of,  248. 

hydroxide,  250. 

native,  247. 

ores  of,  247. 

oxides,  249. 

pyrites,  247. 

reactions  of,  249. 


Copper  sulphate,  171,  249. 

sulphide,  157,  250. 
Copperas,  100. 
Cork-borers,  31. 
Corrosive  sublimate,  252. 
Cupellation,  255,  256. 
Cupric  compounds,  249. 
Cuprous  compounds,  249. 

DECOMPOSITION,  14. 
Definite  proportions,  law  of,  57. 
Deliquescence,  197. 
Diamond,  109. 
Dibasic  acids,  172. 
Diffusion  of  gases,  75. 
Dimorphism,  157. 
Disinfectants,  107,  140,  214,  217. 
Distillation,  60. 

fractional,  64. 
Drinking-water,  59. 
Dutch  metal,  139,  141. 

EFFERVESCENCE,  207. 

Electricity  and  chemical  action,  25. 

decomposition  by,  26,  51-54. 

produces  ozone,  38. 
Element  defined,  24. 

differs  from  compound,  122. 
Elements,  ancient,  41. 

atomic   weights   of,   118,    123, 
124. 

classification  of,  262. 

number  of,  117. 

symbols  of,  118,  123. 

table  of,  118. 
Emerald,  233. 

English  and  French  measures,  286. 
Epsom  salt,  212. 
Equations,  chemical,  127. 
Etching  glass,  150. 
Evaporation,  20. 


294 


INDEX. 


Exercises  in  investigation,  39,  6:3, 

82,  98. 

Experiment,  defined,  10. 
value  in  chemistry,  12. 

FERRIC  CHLORIDE,  144. 

Ferrous  chloride,  144. 

Ferrous  and  ferric  compounds,  226. 

Filter,  20. 

Filtration,  20. 

Fire,  41. 

Fire-damp,  116. 

Flame,  due  to  gas,  45. 

effect  of  cooling,  49. 

oxyhydrogen,  43. 

smoke  of,  42. 

source  of  the  light,  47. 

structure  of,  48. 

tests,  198,  201,  211. 
Flame  color,  to  produce,  198. 
Flint,  183. 

Flowers  of  sulphur,  155. 
Fluorine,  149. 
Fluor  spar,  150. 
Fly  powder,  178. 
Fool's  gold,  154. 
Formulas  of  compounds,  124. 
Fractional  distillation,  64. 
Freezing-point,  63. 
Fuel,  42. 

Furnace,  221,  223. 
Fusible  metal,  235. 

GALENA,  154,  242. 
Gallium,  268. 
Galvanized  iron,  214. 
Gas,  illuminating,  85. 
Gases,  analysis  of,  70,  82. 

burn  with  flame,  45. 

diffusion  of,  75. 

expansion  of,  121. 


Gases,  measurement  of,  71. 

method  of  drying,  31. 

method  of  collecting,  29,  33. 

solubility  of,  59. 
German  silver,  214,  248. 
Glass,  185,  208. 

blue,  220. 

hard  and  soft,  14. 
Gold,  259. 

coin,  260. 

extraction  by  washing,  259. 

extraction    by  amalgamation, 
259. 

properties  of,  259. 
Graphite,  110. 
Green  vitriol,  249. 
Groups,  262. 

analytical,  269. 

natural,  266,  267. 

of  non-metals,  147, 161, 182, 184. 

of  metals,  262-264. 
Grouping  by  atomic  weights,  264. 

by  likeness  of  properties,  263. 

by  solubility  of  compounds, 
264,  268. 

by  valence,  262. 

for  analysis,  269. 
Gypsum,  208. 

HEMATITE,  221.    v 

Heat,  agent  in  chemical  change,  28. 

a  product  of  chemical  change, 
19,  25,  28. 

intensity  of,  44. 

quantity  of,  44. 

unit  of,  32. 
Hydrates,  133. 
Hydrocarbons,  115. 
Hydrochloric  acid,  145. 

composition  of,  146. 

constant  composition,  56. 


INDEX. 


295 


Hydrochloric  acid,  preparation  of, 
145. 

properties  of,  146. 

solubility  of,  58,  59,  146. 
Hydrofluoric  acid,  150. 
Hydrogen,  28-32. 

antimonide  (stibine),  235. 

arsenide  (arsine),  180. 

chloride,  145. 

diffusion,  75. 

explosibility,  30. 

in  nature,  32. 

nitride  (ammonia),  84-88. 

phosphide  (phosphine),  182. 

preparation  of,  19,  28. 

properties  of,  29-32. 

set  free  by  electricity,  26. 

solubility  of,  59. 

sulphide,  158. 

weight  of  a  liter,  32. 
Hydrogen  sulphide,  158. 

preparation  of,  159. 

properties  of,  160. 

use  of,  160. 
Hydroxides,  131. 

names  of,  137. 
Hypophosphorus  acid,  177. 

ICE,  63. 

Ignition  tubes,  14. 
Illuminating  gas,  85. 
Investigation  of  some  chemical  ac- 
tions, 39. 

in  study  of  nitric  acid,  92. 

of  sulphuric  acid  on  iron,  40. 

of  H2  S  O4  on  oxalic  acid,  82. 

other  examples  of,  30,  63,  99, 

173. 
Iodides,  149. 

reactions  of,  161. 
Iodine,  148. 


Iodine,  test  for,  149. 

tincture,  of,  149. 
Iridium,  261. 
Iron, 220-232. 

chlorides,  144. 

combustion  of,  36. 

compounds  of,  226. 

extraction  of,  221. 

galvanized,  214. 

group  of  metals,  217,  231. 

hydroxides,  137. 

manufacture  of  cast,  222. 

manufacture  of  steel,  225. 

manufacture  of  wrought,  223. 

occurrence  of,  220. 

ores  of,  220. 

reactions  of,  226-229. 

sulphate,  170. 

sulphides..  158,  220. 

two  classes  of  salts  of,  226. 

JASPER,  183. 
KINDLING-POINT,  44. 

LABORATORY  SUPPLIES,  279-284. 
Lamp-black,  105. 
Laughing-gas,  96. 
Lavoisier's  experiment,  65. 
Law,  119. 

Avogadro's,  122. 

of  constant  proportions,  57. 

of  multiple  proportions,  97, 123. 

the  periodic,  266. 

the  "two  volume,"  147. 
Lead,  242-246. 

carbonate,  244. 

chloride,  245. 

chromate,  230. 

extraction  of,  242,  243. 

iodide,  246. 

nitrate,  245. 


296 


INDEX. 


Lead,  ores  Of,  242. 

oxides,  244. 

properties  of,  244. 

reactions  of,  245. 

sulphide,  245. 

symbol  of,  242. 
Lead-tree,  243. 
Light,  and  chemical  action,  27. 

of  flames,  46. 

on  nitric  acid,  91. 

oxyhydrogen,  46. 
Lime,  206. 
Lime-light,  46. 
Limestone,  206. 
Lime-water,  207. 

a  test  for  C02l  17. 
Litharge,  244. 
Lithium,  204,  265. 
Lucifer  match,  165. 

MAGNESIA,  212. 
Magnesium,  212. 

carbonate,  212. 

combustibility  of,  13. 

oxide,  212. 

reactions  of,  212. 

sulphate,  212. 
Magnetic  oxide,  220. 
Malachite,  247. 
Malleable  iron,  224. 
Manganese,  217. 

reactions  of,  218. 
Marble,  206. 
Marsh-gas,  116,  184. 
Matches,  165,  176. 
Melting-point,  63. 
Mendelejeff  s  system,  266. 
Metal,  denned,  192. 
Metals,  192. 

and  non-metals,  193,  236. 

analytical  groups  of,  269. 


Metals,  classification  of,  262,  264. 

native,  193. 

number  of,  193. 

occurrence  of,  193. 

of  the  alkalies,  204. 

of  the  alkaline  earths,  210. 

the  calcium  group,  210. 

the  copper  group,  247. 

the  iron  group,  231. 

the  platinum  group,  261. 

the  potassium  group,  204. 

the  zinc  group,  215. 
Metallurgy,  194. 

amalgamation  in,  255,  259. 

cupellatioii  in,  255,  256. 

precipitation  in,  243. 

reducing  ores,  213. 

roasting  ores,  213. 

washing  of  gold,  259. 
Meteoric  stones,  220. 
Methane,  116,  184. 
Metric  measures,  286. 
Mercury,  251-253. 

alloys  of,  251. 

chlorides,  252. 

compounds  of,  252,  253. 

extraction  of,  251. 

ore  of,  251. 

oxide,  14,  252. 

reactions  of,  252. 

sulphide,  253. 
Mineral  waters,  59. 
Mining,  194. 
Minium,  244. 
Mispickel,  179. 
Mixture  defined,  24. 
Molecular  weights,  125. 
Molecules,  121. 
Monobasic  acids,  173. 
Mortar,  207. 
Multiple  proportions,  97. 


INDEX. 


297 


Multiple  proportions,  law  of,  97, 
123. 

NASCENT  STATE,  85. 
Nessler's  reagent,  98. 
Neutral  compounds,  134. 
Neutral  salts,  173. 
Neutralization,  133. 
Newland's  discovery,  264. 
Nickel,  219. 
Nitrates,  92, 

tests  for,  100. 
Nitre,  196. 
Nitric  acid,  90-95. 

decomposition  of,  91,  92. 

preparation  of,  91. 

properties  of,  91. 

test  for,  100. 
Nitric  oxide,  95. 
Nitrogen,.  6<L , 

compounds,  84. 

group,  182.  ^ 

in  plants,  102.  *•" 

oxides,  92-96. 

properties  of,  69. 
Non-metals,  V& 

classification  of,  189,  262. 

the  carbon  group,  184. 

the  chlorine  group,  147. 

the  nitrogen  group,  182. 

the  sulphur  group,  161. 
Nomenclature,  135. 
Normal  salts,  173. 

OBSERVATION,  9. 
Oil  of  vitriol,  166. 
Onyx,  184. 
Opal,  183. 
Ores,  194. 
Osmium,  261. 
Oxidation,  37. 
slow,  175. 


Oxides,  37. 

nitrogen,  96. 

reduction  of,  109. 
Oxidizing  agent,  217,  228. 
Oxygen,  33-39. 

allotropism  of,  38. 

in  nature,  37. 

preparation  of,  14, 16,  33. 

solubility  of,  59. 

test  for,  34. 
Oxyhydrogen  flame,  43. 

blowpipe,  43. 
Ozone,  38. 

PARIS  GREEN,  180. 
Percentage  composition,  55. 
Periodic  law,  266. 
Phosphates,  178. 
Phosphine,  182. 
Phosphoric  acid,  177. 
Phosphorous  acid,  177. 
Phosphorus,  175-178. 

acids,  177. 

action  on  air,  83. 

allotropic  forms,  176. 

burning  of,  67,  68. 

manufacture  of,  178. 

oxides,  177. 

properties  of,  175. 

red,  175. 

salts  of,  178. 
Phosphuretted  hydrogen  (pho< 

phine),  182. 
Photography,  173,  257. 
Pig-iron,  222. 
Plants,  composition  of,  101. 

food  of,  102. 

respiration  of,  81. 
Plaster  of  Paris,  208. 
Platinum,  260. 

group  of  metals,  261. 


298 


INDEX. 


Plumbago,  110. 
Potash,  196. 
Potassium,  195-198. 

action  on  water,  195. 

alum,  233. 

carbonate,  196. 

chlorate,  16,  35. 

chloride,  197. 

group  of  metals,  204. 

hydroxide,  196. 

manganate,  219. 

nitrate,  196,  197. 

occurrence  of,  195. 

permanganate,  217,219. 

reactions  of,  197. 

tartrate,  197. 
Precipitate,  23,  198. 

when  one  will  fall,  210. 
Precipitation  in  metallurgy,  243. 
Prussian  blue,  228. 
Puddling,  223. 
Pyrites,  arsenical,  179. 

copper,  247. 

iron,  154,  158,  220. 

QUARTZ,  183. 
Quick-lime,  206. 

REACTIONS,  126. 

numerical,  127. 

way  to  write,  127, 190. 
Red-lead,  244. 
Red  phosphorus,  175. 
Report  of  analysis,  275, 
Respiration,  77. 

effect  an  air,  79. 

of  plants,  81. 

products  of,  78. 
Reverberatory  furnace,  223. 
Rhodium,  261. 
Roasting  of  ores,  179,  213, 


Rock  crystal,  183. 
Roll  brimstone,  155. 
Rubidicein,  204. 
Ruby,  234. 
Ruthenium,  261. 

SALT,  defined,  131. 
common,  56. 
Salt-cake,  199. 
Saltpetre,  90,  196. 
Salts,  131. 

acid,  173. 

analysis  of,  270-274. 

basic,  245. 

complex,  274. 

names  of,  136,  274. 

preparation  of,  131. 

preparation  by  fusion,  219. 

preparation    by    evaporation, 
210. 

preparation    by  precipitation, 

208. 
Sandstone,  183. 

simple,  274. 
Sapphire,  234. 
Selenides,  161. 
Selenium,  161. 
Silica,  183. 
Silicates,  184. 
Silicic  acid,  184. 
Silicon,  183. 

hydride,  184. 

oxide,  183. 
Simple  salts,  274. 
Silver,  254-258. 

chloride,  22,  27,  257. 

coin,  256. 

compounds  of,  256. 

extraction  from  the  sulphide, 
254. 

extraction  from  galena,  255. 


INDEX. 


299 


Silver,  nitrate,  256. 

ores  of,  254. 

properties  of,  256. 

reactions  of,  257. 

separation  from  copper,  257. 

ware,  256. 
Slag,  222. 
Slaked  lime,  207. 
Slate  rocks,  185. 
Smoke,  42. 
Snow-flakes,  63. 
Soaps,  200. 
Soda-ash,  200. 
Soda-water,  114,  200. 
Sodium,  199-201. 

carbonate,  199. 

chloride,  199. 

hydroxide,  200. 

reactions  of,  201. 

theosulphate,  173. 
Solubility,  210. 
Solution,  58,  59. 
Spiral  of  elements,  266, 
Stalactite,  208. 
Stalagmite,  208. 
Starch-test,  149,  152. 
Steel,  224. 
Stibine,  235. 
Strontium,  210. 

reactions  of,  211. 
Sublimation,  204. 
Substitution,  19. 

governed  by  valence,  189. 
Sugar,  solubility  of,  10. 

action  with  sulphuric  acid,  11. 
Sulphates,  170. 

ways  to  make  the,  172. 
Sulphides,  154. 

artificial,  157. 
Sulphur,  154-163. 

combustion  of,  18, 67, 68. 


Sulphur,  crystals  of,  156. 

dioxide,  18,  163. 

effect  of  heat  on,  155. 

flowers  of,  155. 

group,  161. 

native,  154. 

preparation  of,  154. 

roll,  155. 

Sulphuretted  hydrogen,  159. 
Sulphuric  acid,  166-170. 

action  on  copper,  163,  171. 

action  on  iron,  40. 

action  on  oxalic  acid,  82. 

action  on  sugar,  11. 

action  on  water,  25. 

action  on  zinc,  170. 

manufacture  of,  168. 

properties  of,  166. 

test  for,  167. 

uses  of,  167. 
Sulphurous  acid,  165. 
Sulphurous  oxide,  163. 
Sulphur  springs,  159. 
Supplies,  chemical,  284. 
Symbols,  123. 
Synthesis,  24,  50. 

TABLE,  blank,  for  the  analytical 

groups,  269. 
of  symbols  and  atomic  weights, 

118. 

of  French  and  English  meas- 
ures, 286. 
of  the  periodic   system  in  a 

spiral,  267. 

Temperature,  rule  to  change  Cen- 
tigrade to  Fahrenheit  degrees, 

287. 
rule  to  change  Fahrenheit  to 

Centigrade  degrees,  287. 
Theory,  120. 


300 


INDEX. 


Theory,  atomic,  123. 

Avogadro's,  122. 

distinguished  from  facts,  121. 

of  matter,  121. 
Tin,  239-242. 

chlorides,  240. 

compounds  of,  240. 

extraction  of,  239. 

foil,  240. 

ore  of,  239. 

properties  of,  239. 

reactions  of,  241. 

sulphides,  241. 

ware,  240. 

Tincture  of  iodine,  149. 
Tin-foil,  240. 
Tinstone,  239. 
Tin-ware,  240. 
Topaz,  233.  { 

Type-metal,  235. 

UNIT  of  heat,  32.      » 

VALENCE,  188-191. 

a  property  of  atoms,  188. 

denned,  189. 

described,  189. 

measured,  189. 

represented,  189. 

governs  substitution,  189. 

governs  reactions,  190. 

in  classification,  189,  262. 

of  boron,  190. 

variation  in,  191. 
Ventilation,  80. 
Vermilion,  251. 
Vitriols,  166,  249. 
Volume,  changed  by  heat,  71, 121 

changed  by  pressure,  71, 121. 

composition  by,  147. 

of  ammonia,  90. 

of  hydrochloric  acid,  146. 


Volume,  of  nitrogen  oxides,  147. 
of  water,  56. 
the  law  deduced,  147. 

WATER,  50-64. 

analysis  of,  61. 

a  product  of  combustion,  41. 

a  product  of  respiration.  78. 

as  a  solvent,  58. 

boiling-point  of,  61. 

composition  of,  55,  56. 

distillation  of,  60. 

drinking,  59. 

freezing-point  of,  63. 

greatest  density  of,  62. 

hard  and  soft,  59. 

in  Ahe  air,  74. 

in  nature,  57. 

mineral,  69. 

of  crystallization,  186. 

synthesis  of,  31,  36. 
Weights,  atomic,  118, 124. 

combining,  98. 

metric  and  English,  286. 

molecular,  125. 
White  lead,  245. 
White  vitriol,  214. 
Wrought-iron,  223. 

ZINC,  212-216. 

amalgamated,  26. 

chloride,  21,  214. 

compounds  of,  214. 

group  of  metals,  216. 

manufacture  of,  213. 

ores  of,  212. 

reactions  of,  214. 

sulphate,  170. 

sulphide,  161,  215. 

uses 

Zincite, ! 
Ztnc  \thlte,  214 

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